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Volume 37, 1904
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Art. XIII.—Report on the Mollusca collected by Messrs. Keith Lucas and G. L. Hodgkin in Six Lakes of New Zealand.

[Read before the Wellington Philosophical Society, 7th September, 1904.]

During the year 1902 Messrs. Keith Lucas and G. L. Hodgkin, of Cambridge, made a collection of the fauna of a typical series of lakes in New Zealand, most of the Mollusca being obtained by dredging. Before reaching New Zealand Mr. Lucas had promised Mr. Charles Hedley, conchologist of the Australian Museum, Sydney, to hand him over the Mollusca which would be obtained from our lakes for study, but later on, with Mr. Hedley's consent, the whole of the material was handed over to me. My very best thanks are due to Messrs. Lucas and Hodgkin for allowing me to study the interesting collection, and to my friend Mr. Hedley for his most readily given consent.

Mr. Lucas has published in the Geographical Journal for May and June, 1904, a highly interesting and beautifully illustrated report on the “Bathymetrical Survey of the Lakes of New Zealand,” and Professor W. B. Benham, of Dunedin, has published* the result of his study of the aquatic Oligochæta collected by Messrs. Keith Lucas and Hodgkin.

The lakes from which Mollusca were handed over to me are the following: North Island—Waikare, Rotoiti, Taupo, Waikaremoana; South Island—Wakatipu, Manapouri.

With regard to the deep-water Mollusca of our lakes nothing at all was known, all the collecting hitherto done having been confined to shallow water, and mostly, of course, near the shore. To show how scanty our knowledge of the molluscan fauna of the above-named lakes has been, it may be of interest to mention that the following species have been recorded: Lake Rotoiti—Sphœrium novæ-zelandiœ, Desh. (as lenticula, Dk.), Potamopyrgus badia, Gould (as fischeri, Dk.), both collected by Hochstetter, and Melanopsis trifasciata, Gray. Lake Taupo—Diplodon menziesi, Gray (Dieffenbach), and its subsp. hochstetteri, Dk. (Hochstetter). Lake Waikaremoana—Diplodon menziesi, Gray (as waikarense, Colenso). Lake Wakatipu—Planorbis corinna, Gray, and Isidora antipodea, Sow., both collected by Captain F. W. Hutton.

I propose to describe first, in systematical order, all the molluscs brought together, then to give a synopsis of the molluscan fauna of each lake, and finally tabulate the bathymetrical distribution of the species.

[Footnote] * P.Z.S., 1903, vol. ii., pp. 202–232, pls. xxiv.-xxvi.

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Fam. UnionidÆ.

Genus Diplodon, Spix (1827).

Shell elliptical, rounded, elongated or trapezoidal, with rather low beaks which are more or less distinctly radially sculptured, the ridges usually curved and approaching below, with a low or scarcely developed posterior ridge; surface slightly concentrically sculptured, sometimes broken into fine nodules or corrugations; epidermis dull, rayless; hinge with two compressed pseudocardinals in the right valve, and one slender lateral, and two compressed pseudocardinals in the left valve, one in front of the other, and two laterals; nacre bluish to white, dull, often blotched; beak-cavities shallow; dorsal scars numerous, forming a row in the beak-cavity parallel with the hinge line.

Animal with the marsupium occupying nearly the whole length of the inner branchiæ, a few ovules sometimes being found in the outer gills; branchiæ rather large, angular at base, inner much the larger, united their whole length to the abdominal sac; palpi scarcely projecting posteriorly; mantle very thin, thickened on the edges; branchial opening papillose, separated from the smooth anal opening by a strong bridge; supra-anal opening not closed below. (Simpson.)

Type: D. ellipticum, Spix.

Subgenus Hyridella, Swainson (1840).

Beaks rather low, sculpture consisting of curved generally nodulous ridges, which approach below, but usually have a smooth area of shell between them; surface sulcate or sometimes corrugated and nodulous; epidermis rayless; teeth rather delicate, compressed, often somewhat rudimentary.

Animal having the embryos occupying the inner gills for the most part, which are united for their entire length to the abdominal sac; outer gills pointed below in the middle; palpi triangular; branchial opening papillose; anal opening smooth, not separated from the supra-anal opening. (Simpson.)

Type: Unio australis, Lamarck.

Diplodon menziesi, Gray (1843).

Unio menziesi, Gray, in Dieffenbach's “New Zealand,” vol. ii., 1843, p. 257. Unio aucklandica, Gray, l.c., p. 257. Unio waikarense, Colenso, Tasman. Journ. Nat. Sci., vol. ii., 1845, p. 250.

I am following C. Simpson in considering Unio aucklandica as a synonym only. On examining a rather large series of specimens from over twenty localities I tried to uphold it at least as

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a subspecies, but I had to give it up, as I had numerous specimens before me which could be either assigned to menziesi or to aucklandica. There is no doubt that when the extreme forms only are compared one would feel inclined to take them for distinct species, but so it is with many other species, as for instance with Helcioniscus tramosericus. However, it is convenient to refer to aucklandica as a form of menziesi which is but little winged, and having the dorsal and ventral margins subparallel.

Unio waikarense will be dealt with further on when describing the mussels from Lake Waikaremoana.

(1.) Lake Taupo (Stat. 9—From dredgings up to 100 ft.).—There are eight specimens, representing quite young to half-grown forms, only one being highly winged. All are distinctly radiately striate, and some of the youngest specimens show the typical beak-sculpture beautifully. It is represented by the accompanying diagram (fig. 1). One of the larger specimens is very distinctly sculptured with elongate nodules on the lower half down to the ventral margin in the region below the beaks. The interior and hinge are the same as in specimens of subspecies hochstetteri, to be described further on. The largest specimen measures—Length, 42 mm.; height, 28 mm.; diam., 13 mm.

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Fig. 1

(2.) Lake Taupo (Stat. 9F—From dredgings up to 100 ft.).—The eight specimens have the same appearance as those of the last station; all of them have the outline of aucklandica, are finely radiately striate, and one clean olive-coloured specimen also shows nodulous ornamentation. Five quite young specimens have the beaks already so much eroded that no trace of the beak-sculpture is left. A few specimens have a light ferrugineous coating. The largest specimen shows—Length, 43 mm.; height, 28 mm.; diam., 13 mm.

(3.) Lake Waikaremoana (Stat. 14—Dredged in 50 ft.).—Compared with the type of Unio waikarense, Colenso, said to have been obtained in this lake, the four specimens collected at this station are much smaller, very little winged posteriorly, the dorsal margin subparallel to the ventral, darker in colour, and more solid; they are not concentrically sulcated, but only striated, and the marks of rest are much less distinct. All of them are finely radiately striated, a character always to be found in menziesi. The pseudo cardinals are typical, the upper lateral tooth in the left valve is much lower than the other, and crenate

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in all specimens. Inside bluish-white, pearly, blotched with yellowish, especially in the umbonal cavity.

(4.) Lake Waikaremoana (Stat. 37—Dredged in 15 ft.).—Four specimens of different size, showing all the characters of those from Stat. 14.

In some specimens in my collection, kindly sent to me by Mr. Elsdon Best, and collected in Lake Waikaremoana, the radiate sculpture is distinctly nodulous, sometimes V-shaped, thus approaching D. websteri, Simpson. Typical specimens of aucklandica from creeks near Auckland show the same sculpture to a most marked degree, and I consider D. websteri as a D. menziesi in which the nodulous sculpture is developed to the highest degree.

I have seen, thanks to Mr. E. Best's great kindness, a large number of Diplodon from Lake Waikaremoana, but not one approaching Colenso's type of waikarense, which is a large, thin, yellowish-olive-coloured shell, having more the appearance of an Anodonta. The Waikaremoana specimens are all much smaller, thicker, darker in colour, and less winged. Mr. A. Hamilton, Director of the Colonial Museum, to whom I spoke about it, and who has visited the locality, suggests that Colenso did not get his specimens from Lake Waikaremoana itself, but from some small lake or lagoon in the vicinity. This seems to be correct, as I obtained, again through the unremitting kindness of Mr. E. Best, a number of specimens from a lagoon near Ruatoki, Tuhoeland, and these are typical waikarense, Colenso; one of them showing the same outline and the same dimensions as the cotype in the Canterbury Museum.

An error in Colenso's diagnosis of Unio waikarense (Trans. N.Z. Inst., xiv., 169) wants correcting. He says, “Posterior slope keeled.” This, however, is not correct: the shell is not keeled. How misleading such an incorrect statement is may be guessed from Simpson's remark on the species in his “Synopsis of the Naiades,” p. 890 (footnote): “Suter thinks this is a variety of menziesi, but Colenso states that the posterior slope is keeled. If this is so it must be quite different from the species.” There is also an error in the quotation in Simpson's work, as he gives the year 1841 as the date of the publication of the Tasman. Journ. Nat. Sci. vol. ii., whereas it is 1845. Colenso says that he discovered the shell in 1841, but his description was published four years later.

I have compared typical specimens of waikarense with many specimens of menziesi from about twenty different localities, and I am unable to separate the two. In all essential characters the two agree, and there remains nothing but to make Colenso's species a synonym of D. menziesi, Gray.

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Diplodon menziesi, Gray, subsp. hochstetteri, Dunker (1862).

Unio hochstetteri, Dunker, Malak. Blätter, vol. viii., 1862, p. 153.

The type was collected by Hochstetter in the Waikato River.

(1.) Lake Taupo (Stat. 46—From dredgings in 10–30 ft.).—Six specimens, blackish-brown, much corroded round the beaks, most of them more produced and rounded posteriorly than the type, but some have the posterior end distinctly truncated and more or less biangular. In correspondence with Mr. C. T. Simpson I expressed the opinion that hochstetteri is a pathological subspecies,* having seen the same form amongst specimens of rugatus, Hutton, from the Kopuaranga River, and also amongst menziesi from the River Avon. The young shells are invariably typical D. menziesi, but on growing larger the deformity constituting hochstetteri becomes more and more apparent. Some specimens are more affected, others less, thus producing a strongly truncated biangular posterior margin, or it remains only flatly rounded. At the posterior end the periostracum is produced in thick, foliated layers, and the inner margin is considerably thickened by pearly substance, forming large rugosities, and very often pearls adhering to the shell are met with. Loose small pearls of irregular form are only exceptionally found. In my opinion the cause of this is most likely some parasitic creature, as is the case in most of the pearl-producing bivalves. The outer exposed layers round the beaks are smooth, light-brown, waxy. The concentric striation is rather coarse, the marks of rest distinct and elevated. The inside is but little iridescent, except along the ventral margin, outside the mantle impression, grey to light-brown, sometimes blotched with brown; there are more or less considerable rugosities beyond those at the posterior margin. The dorsal scars in the umbonal cavity are small and deep, and to the number of two to four. The anterior adductor impressions are irregular in shape, and much deeper than the posterior ones, which are oval and shallow. Right valve with two pseudocardinals, the upper anterior forming a small lamella, the posterior being strong, compressed, high, triangular, and slightly corrugated. The single lateral tooth is regularly slightly curved and somewhat crenate at its posterior end, which is abruptly descending. Left valve with two pseudocardinals arising from a common base, both blunt, the anterior tooth larger and but slightly crenate. The two laterals are also curved, the lower of them is strongly lamellated and denticulated at its posterior end, which slopes down very gradually.

[Footnote] * C. T. Simpson, “Synopsis of the Naiades,” p. 889 (footnote)

[Footnote] † Trans. N.Z. Inst., xxiv., 275.

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(2.) Lake Rotoiti (Stat. 8—Obtained by dredging in 12 ft.).—Two specimens of medium size, strongly concentrically ridged, umbones much eroded, posterior end subtruncated, not yet distinctly biangular. They represent the intermediate stage between the young menziesi and the full-grown hochstetteri. Interior olive-bluish, pearly, a row of small dorsal scars in the umbonal cavity, parallel to the hinge line. Muscular scars strongly impressed. Right valve with two very unequal pseudo-cardinals, the anterior small, lamellar, the posterior compressed, with a broad posterior base, crenulated, trifid; the lateral tooth slightly curved, narrow, high, truncate and corrugate posteriorly. Left valve with the two pseudocardinals coalescent, separated only by a groove, the anterior strong, triangular, rugose. The two laterals with crenate edges, obliquely truncated behind. The dimensions of the two specimens are—Length, 50 mm.; height, 34 mm.; diam., 16 mm.; and, length, 41 mm.; height, 29 mm.; diam., 12.5 mm.

Diplodon menziesi, Gray, subsp. rugata, Hutton (1883).

Unio rugatus, Hutton, N.Z. Journ. Sci., vol. i., 1883, p. 478.

Lake Waikare (Stat. 41—From dredgings in all parts of the lake; most common on sand and on stony shore).—Six specimens, two of which are quite young. The latter are winged posteriorly, the beaks already eroded, and there are three to six nodulous ridges descending in front of the umbo, nearly parallel to the anterior margin; they are concentrically finely thread-striated; colour olive-brown; the inside is bluish-pearly, yellow under the beaks. The larger specimens are subventricose and thin, less winged, the dorsal margin nearly parallel to the length-axis; the beaks are corroded, the anterior margin rounded, sometimes slightly truncate, the posterior margin produced and the ventral margin broadly convex. The concentric striae are irregular, rugose posteriorly, fine and more regular at the anterior end; the marks of rest are fairly distinct. Most of the specimens are partly covered with a dark-brown ferrugineous coating. Interior bluish, yellowish, or purple pearly, sometimes strongly blotched with olive. Muscular scars shallow. Right valve with two compressed triangular pseudocardinals close together, the anterior tooth smaller, lamellar and smooth, the posterior stronger, broader, and somewhat rugose. The lateral tooth is slender, curved, rugose on the edge of the posterior part. Left valve with two elongated, rounded, rugose pseudocardinals which sometimes coalesce, when only a slight notch indicates the original two teeth. The two laterals are long, slender, sinuate, and distinctly pectinate at the posterior edges. There are always a few small rather deep dorsal scars in the umbonal cavity.

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Diplodon menziesi, Gray, n. subsp. lucasi.

Lake Manapouri (Stat. 35—Dredging in 60 ft.).—Three specimens; one of them may be taken as adult. Shell (figs. 2 and 3) oblong-ovate, very much compressed, thin and fragile, inequilateral, beaks low, eroded; surface with close strongly pronounced rest-marks and between them a few lines of growth, all close together and foliated at the anterior end. In the adult specimen the middle part has distinct radiate nodulous sculpture, partly V-shaped, but no such ornamentation is to be found on the young specimens. The straight dorsal margin is subparallel to the ventral margin, which is slightly sinuate; the anterior margin is angularly rounded, the posterior obliquely truncated and slightly produced. Nearly the whole of the shell is covered with a thin ferrugineous coating; the epidemis is olive-green, waxy. The ligament is small, not much raised. In the right valve the two pseudocardinals are compressed, small; the upper anterior tooth is a small, smooth lamella, the lower tooth is more elevated, conoidal, and strongly crenate; the lateral tooth is almost straight, thin and rugose at its posterior portion. In the left valve there is a rather long compressed lower anterior rugose pseudocardinal, the upper tooth is quite rudimentary; the upper lateral tooth is a little higher and more rugose posteriorly than the other. Interior bluish-white, pearly, a little blotched with olive in the umbonal cavity, where there are rather large and deep dorsal scars. The adductor-muscle scars are shallow. The young specimens are slightly winged.

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Fig. 2

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Fig. 3

This subspecies is nearest to the typical aucklandica, but is distinguished from it by its exceptionally compressed form, the thinness of the shell, the strongly marked and close concentric lines, the more tapering posterior margin, and the feebly developed pseudocardinals. The radiate nodulous sculpture is found in many specimens of menziesi and its subspecies. Adult specimen—Length, 45 mm.; height, 24 mm.; diam., 8 mm.

Type in my collection.

I have much pleasure in naming the subspecies in honour of its discoverer, Mr. Keith Lucas.

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Diplodon lessoni, Küster (1856).

Unio lessoni, Küster, Conch. Cat., 1856, p. 135, pl. xxxvi., fig. 4. Type from New South Wales.

Lake Wakatipu (Stat. 37—Dredged in 10 ft. to 30 ft.).—Nine specimens were obtained. Shell (fig. 4) oblong, obliquely truncated behind, compressed, inequilateral, beaks strongly eroded in all specimens, no trace of sculpture left; surface with distant flatly elevated rest-marks, which, together with the intervening space, are covered with very fine thread-like concentric lines; towards the base and posterior margin the growth-lines are more distinct and slightly foliated. There is no trace of radial sculpture. The epidermis is olive to dark-brown, dull. Interior bluish nacre, with yellowish patches under the beaks, where there are several deep small dorsal scars. Right valve: The pseudocardinals are compressed, the anterior upper tooth is small, grooved, the posterior tooth much larger and crenate; the lateral tooth is slightly arched and rugose posteriorly. Left valve: Anterior pseudo-cardinal compressed, tongue-shaped, slightly rugose, the posterior subtriangular, deeply denticulate; the laterals are of nearly equal height and crenate posteriorly.

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Fig. 4

The largest specimen was selected for the diagram and description, and its dimensions are—Length, 51 mm.; height, 30 mm.; diam., 14½ mm.

I submitted specimens to Dr. W. H. Dall, Hon. Curator of Mollusks, U.S. Nat. Museum, for examination, and he very kindly informed me that according to the material in the museum they are D. lessoni, Küster. I have not seen any Australian specimens, nor the description and figure published by Küster, but I do not hesitate to accept Dr. Dall's view, although some may think it hazardous to refer our shell to a New South Wales species. I have not seen this species from anywhere else in New Zealand.

Dr. Von Jhering once suggested that a number of measurements should be taken to ascertain the range of variability in species of the family Unionidœ. I have measured a great number of specimens from New Zealand some years ago, and may publish the results later on. I have done the same for a number of the Unionidœ collected by Messrs. Lucas and Hodgkin, and

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the result is contained in the following table. [The ciphers i. to xi. in the table indicate—i. Length of shell. ii. Greatest height. iii. Index of height (length = 100, height in % of it). iv. Distance of greatest height from anterior end. v. Index of position of greatest height (length = 100, distance of greatest height in % of it). vi. Diameter. vii. Index of diameter (length = 100, diameter in % of it). viii. Length of hinge line. ix. Distance of beak from anterior end of hinge line. x. Umbonal index (length of hinge line = 100, distance of beak from anterior end of hinge line in % of it). xi. Cardinal index (length of shell = 100, length of hinge line in % of it).]

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

i. ii. iii. iv. v. vi. vii. viii. ix. x. xi.
D. menziesi.
Taupo, 9 32 19 59 9 28
" 9F 37 23 62 10 27
Waikaremoana, 14 44 28 64 23 52 13 29 32 9 28 72
" 14 41 23 56 25 61 10 24 25 6 24 61
" 14 39 22 56 21 53 10 27 24 6 25 61
Mean of the three above 41 24 58 23 55 11 27 27 7 25 64
Waikaremoana, 37 55 32 58 30 54 18 32 38 10 26 69
" 37 60 33 55 28 47 17 28 40 10 25 67
" 37 61 36 59 31 50 19 31 40 10 25 66
" 37 62 33 53 31 50 19 30 40 10 25 64
Mean of the four above 59 33 56 30 50 18 30 39 10 25 64
Cotype of waikarense 79 48 61 40 51 25 31 47 10 21 59
D. hochstetteri.
Taupo, 46 48 31 65 24 50 16 33 36 24 75
" 46 52 36 70 30 58 18 35 35 8 23 67
" 46 54 36 67 30 56 19 35 40 10 25 74
" 46 64 40 63 33 52 22 34 48 11 23 75
Mean of the four above 55 38 66 29 54 19 34 40 24 72
From Lake Rotorua, typical 61 44 72 32 52 24 39 42 10 24 69
D. rugata.
Waikare, 41 47 28 59 22 47 14 29 31 8 26 66
" 41 46 29 63 26 56 15 32 30 8 26 65
" 41 44 26 59 20 45 13 29 25 26 57
" 41 41 25 61 21 51 13 31 29 8 27 70
Mean of the four above 44 27 60 22 50 14 30 29 8 26 64
From Lake Pearson, cotype 52 33 63 26 50 17 32 35 9 25 67
D. lucasi.
Manapouri, 35 45 24 53 19 42 8 18 28 8 28 62
" 35 34 21 61 16 47 8 23 22 7 31 64
" 35 28 17½ 62 15 53 23 18 5 28 64
D. lessoni.
Wakatipu, 37 51 30 58 23 45 14½ 28 35 9 26 68
" 37 44 24 58 22 53 11½ 28 26 28 63
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Fam. Sphæriidæ.

Cardinal teeth not exceeding two in each valve, and exhibiting a cessation of development at an early stage. (Dall.)

The New Zealand species of Sphærium and Corneocyclas are not easily separated with regard to their generic position, as both are about to the same extent inequilateral, though in Corneocyclas the anterior part is mostly more attenuated and the nepionic shell sometimes more conspicuous than in Sphærium. The cardinal teeth are very variable, and it is a tedious job to ascertain the genus from these alone, but they assist in the general diagnosis. To be absolutely certain living specimens should be examined, Sphærium having two siphonal tubes, Corneocyclas only one; but with the specimens to be described that was out of the question. Fortunately I have specimens of both genera from New Zealand in my collection, which I examined when alive, and these were of great help to me for the study of the various specimens collected by Messrs. Lucas and Hodgkin.

Much useful information was obtained from the chapter on the family Sphæriidæ in the classical work of Dr. W. H. Dall, “Tertiary Fauna of Florida.”

The indices I calculated for the Sphæriidæ are part of those used for the Unionidœ: iii. = index of height; vii. = index of diameter; x. = umbonal index.

Genus Sphærium, Scopoli (1777).
Subgenus Sphærium, Scopoli, s.s.

Type: S. corneum, Linné.

The nepionic shell passing into the adult without any distinct demarcation; the anterior end shorter; the ligament subinternal; the two right cardinals widely divergent and coalescent at their adjacent or upper ends, thus apparently forming but one tooth, but which if it had continued in development would have separated into two; the widening of the ventral angle causes the A-shape to disappear; the nepionic shell (and consequently the beaks) is finely concentrically striate or even nearly smooth and rather convex. (Dall.)

Sphærium novæ-zelandiœ, Deshayes (1853).

Cat. Conchif. Brit. Museum, p. 272; P.Z.S., 1854, p. 342.

(1.) Lake Rotoiti (Stat. 15—From muddy bottom and weeds in 6 ft.).—Three specimens of nearly equal size, suborbicular, subequilateral; colour grey, near the ventral margin yellowish; beaks covered with a ferrugineous incrustation. Nepionic shell

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hardly to be distinguished from the later growth, obtuse; anterior side of shell slightly produced, rounded, posterior side broadly convex; the whole of the valves concentrically finely striate. Ligament inset. Left valve with a straight lamellar upper cardinal, and below and slightly in front of it a curved stouter tooth. In the right valve the two cardinals are united, forming an oblong squarish tooth with three denticulations on the lower margin. Laterals smooth. Fig. 5 illustrates the cardinal teeth of the two valves. Length, 5 mm.; height, 4¼ mm.; diam., 2¾ mm. Umbo 3 mm. from anterior end. The indices are—iii. = 85; vii. = 55; x. = 60.

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Fig. 5

This is no doubt the same as S. lenticula, Dunker, as Hochstetter obtained the specimens from the lakes Rotoiti and Taupo, and I consider it as a synonym of S. novæ-ze-landiæ.

(2.) Lake Taupo (Stat. 4—Dredged with weeds in 20 ft., and from bottom of coarse pumice in 100 ft.).—Four specimens of straw colour, the nepionic shell rather distinct, but otherwise not differing from the typical form. Right valve with two minute cardinals, the anterior oblong, the posterior short, triangularly oval, elevated. Left valve with two minute teeth, broadly rounded behind, pointed at the anterior end, one in front of the other. Fig. 6 shows the form and position of the cardinals. Length, 4½ mm.; height, 4 mm.; diam., 2½ mm. Umbo 2¾ mm. from anterior end. Indices—iii. = 84–89; vii. = 56; x. = 61.

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Fig. 6

(3.) Lake Taupo (Stat. 34—With weeds from 20 ft. to 80 ft.).—Six small specimens, a little more oval and compressed, but otherwise the same as the examples from Stat. 4. Length, 4 mm.; height, 3 mm.; diam., 1¾ mm. These are the dimensions of Dunker's S. lenticula. Indices—iii. = 75; vii.—44.

(4.) Lake Waikaremoana (Stat. 33—Dredged in 10 ft. to 20 ft.).—There are twenty-three small to minute specimens. The larger examples are yellowish-grey, the small ones straw-colour. In the right valve there are two lamellar cardinal teeth meeting at an obtuse angle; in the left valve there is one crescent-shaped

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rounded cardinal, and a strong bifid crenulated cardinal below and slightly in front of it. Fig. 7 illustrates the cardinals of the valves. The lateral teeth are smooth; the ligament inset. Dimensions of two specimens—Length, 4¼ mm.; height, 3½ mm.; diam., 2 mm.; beak 2½ mm. from anterior margin: length, 4 mm.; height, 3½ mm.; diam., 2 mm.; beak 2¼ mm. from anterior margin. The mean of the indices is—iii. = 85; vii. = 49; x. = 58.

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Fig. 7

Genus Corneocyclas, Férussac (1818).

(= Pisidium, Pfeiffer, &c.)

Subgenus Corneocyclas.

Nepionic shell convex, concentrically striated; hinge with two separate cardinals in the left, and a single compound, usually arcuate, cardinal in the right valve. (Dall.)

Sec. Corneocyclas, s.s.

Type: Tellina pusilla, Gmelin.

Nepionic valves passing into the mature disc without any strong demarcation; the anterior cardinal and lateral adjacent and retaining traces of their original connection; ligament internal. (Dall.)

Corneocyclas novozeelandica, Prime (1862).

P.Z.S., 1862, p. 3.

(1.) Lake Waikare (Stat. 29—From weeds in 1½ ft. to 2 ft.).—Nine specimens of different size; colour greyish-yellow, shining, inequilateral, with fine concentric lines, which are crossed by close microscopic radiate striæ. Nepionic shell convex, concentrically striated, well delimited, but passing without any change into the disc of the adult valve. Ligament inset. Right valve with the two cardinals remaining united, crescent-shaped; four laterals. Left valve with two cardinals, the posterior bifid, the anterior triangular; two laterals. The accompanying fig. 8 shows the characters of the hinge.

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Fig. 8

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Four specimens were measured—Length, 2¾–5 mm.; height, 2½–4 mm.; diam., 1¼–2½ mm.: and the mean indices are—iii. = 83; vii. = 48; x. = 59.

These specimens are very much like those I collected in the River Avon, Christchurch.

(2.) Lake Waikare (Stat. 29F—From weeds in 1½ ft. to 2 ft.).—Four specimens, dead when collected. They do not differ much from those of Stat. 29, except being slightly more globular. The dimensions of three specimens measured are—Length, 5 mm.; height, 4½ mm.; diam., 3¼ mm.; umbo 3 mm. from anterior margin: length, 4¼ mm.; height, 3½ mm.; diam., 2¼ mm. umbo 2½ mm. from anterior margin: length, 3 mm.; height, 2½ mm.; diam., 1½ mm.; umbo 1¾ mm. from anterior margin. The mean indices are—iii. = 85; vii. = 56; x. = 58.

(3.) Lake Wakatipu (Stat. 17—Dredged with weeds in 20 ft. to 100 ft.).—One minute specimen, rounded, yellowish-white, subequilateral. Length, 2¼ mm.; height, 2 mm.

This small specimen has the aspect of a Sphærium, but the nepionic shell is so distinct that I prefer placing it in Corneocyclas for the present. I tried to separate the valves, but could not do it without running the risk of breaking the valves. Without ample material, and especially examining the living animal, it is impossible to be quite certain about its generic position.

(4.) Lake Wakatipu (Stat. 34—Dredged in 10 ft. to 30 ft.).—One adult and four young specimens. The adult is light-brown, the nepionic shell distinctly limited; the young examples are grey to yellowish, more inequilateral and tapering in front. The dimensions of two specimens are—Length, 5¼ mm.; height, 4½ mm.; diam., 2½ mm.; umbo 2¾ mm. from anterior end: length, 3½ mm.; height, 1¾ mm.; diam., 1½ mm.; umbo 2 mm. from anterior end: and the mean indices are—iii. = 83; vii. = 46; x. = 55.

There is one specimen, covered with a black coating, which is suborbicular, much compressed, inequilateral, with inconspicuous beaks, the anterior side broadly rounded. The dimensions are—Length, 4 mm.; height, 3¼ mm.; diam., 1½ mm.; umbo 2½ mm. from anterior end: and the indices are—iii. = 81; vii. = 38; x. = 62. I have seen similar abnormities amongst specimens I collected in the River Avon.

(5.) Lake Manapouri (Stat. 13—Dredged in shallow water near the shore).—Three young specimens, which are at once recognised as being Corneocyclas, being more inequilateral, compressed and attenuated anteriorly than adult specimens. Had I not seen the same forms from other localities, collected together with adult examples, I might have been inclined to consider

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them a distinct species. With few exceptions the young shells of C. novozeelandica show the characters just indicated. The colour is light-grey, and the nepionic shell is distinct. The dimensions of two specimens are—Length, 3¼ mm.; height, 2¾ mm.; diam., 1½ mm.; umbo 2 mm. from anterior end: length, 2¾ mm.; height, 2 mm.; diam., 1 mm.; umbo, 2 mm. from anterior end. The mean indices are—iii. = 78; vii. = 41; x. = 66.

Corneocyclas hodgkini, n. sp. Fig. 9.

(1.) Lake Waikaremoana (Stat. 18—Dredged in 800 ft.).—Two specimens. They are very small, oval, much compressed, the anterior side produced and attenuated; posterior and ventral margins regularly rounded; colour yellowish-white; beaks obtuse, unconspicuous; nepionic shell distinct, very finely concentrically striated, passing without change into the adult valves, which are irregularly finely concentrically striate. Posterior part with a ferrugineous coating. The dimensions are—Length, 2¾ mm.; height, 2 mm.; diam., 1 mm.; and the indices—iii. = 72; vii. = 36: length, 2 mm.; height, 1¾ mm.; diam., ¾ mm.; and the indices—iii. = 87; vii. = 50.

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Fig. 9

Named in honour of Mr. G. L. Hodgkin, who so ably assisted Mr. Lucas in his arduous work.

Type in my collection.

(2.) Lake Taupo (Stat. 10—Dredged in 280 ft. and 320 ft., muddy bottom).—Six small specimens, thickly coated all over with ferrugineous earth, so that the form of the shell is unrecognisable. I succeeded in cleaning one specimen, and found it to agree with the specimens just described from Lake Waikaremoana. Dimensions of the cleaned specimen—Length, 3 mm.; height, 2¼ mm.; diam., 1 mm.

Fam. HydrobiidÆ.

Genus Potamopyrgus, Stimpson (1865).

Americ. Journ. Conch., vol. i., 1865, p. 53.

Potamopyrgus corolla, Gould (1847).

Melania corolla, Gould, Proc. Bost. Soc. Nat. Hist., vol. ii., 1847, p. 223.

(1.) Lake Waikare (Stat. 19—From reeds).—One specimen, with black coating and six rounded whorls. Length, 5½ mm.; breadth, 3¾ mm.

(2.) Lake Taupo (Stat. 16 and 16F—Dredged in 280 ft. and 320 ft., muddy bottom).—Four specimens, all of which are

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shouldered and with traces of stout setæ; covered with a dark-brown coating; there are seven whorls, the peritreme is continuous. The dimensions range from 7 × 4½ mm. to 6½ × 4½ mm.

Potamopyrgus corolla, Gould, subsp. salleana, Fischer (1860).

Paludestrina salleana, P. Fischer, Journ. de Conch., vol. viii., 1860, p. 208, pl. iv., fig. 6.

(1.) Lake Waikare (Stat. 14 and 14F—Among reeds).—From Stat. 14 are thirteen adult and a number of young shells; from Stat. 14F twelve specimens, exactly the same as the former. Most of them are of horn-colour, with a white calcareous coating; three only are coated with black. All, with the exception of one, are spinous, the spines being distant, rather short, bent upward. In some specimens a distinct angle below the periphery is present. All the adult shells are smaller than the type, with six whorls. The dimensions range from 4½ × 2½ mm. to 5¼ × 3¼ mm.

(2.) Lake Rotoiti (Stat. 18—Dredged with weeds in 6 ft.).—Seventeen specimens of rather uniform size and shape, covered with a greenish-black coating. There are five rounded smooth whorls; only one specimen shows traces of bristles on the upper whorls. The peritreme is sometimes, not always, black. A few specimens are approaching corolla, being more ventricose than the subspecies. The dimensions vary from 5 × 3 mm. to 6 × 4 mm.

(3.) Lake Rotoiti (Stat. 18F—Dredged with weeds in 6 ft.).—Sixteen specimens, all “dead shells.” Very much the same as the preceding. Dimensions range from 5 × 3 mm. to 5½ × 3¼ mm.

(4.) Lake Taupo (Stat. 6—Dredged in 25 ft. to 420 ft.).—Many specimens, all light-horn colour, about two-thirds with smooth rounded whorls, the others with a carina above the periphery on which very short spines are situated, having a broad base, from which two to three separate spines arise. This is a feature met with in specimens of P. corolla from Lake Kanieri, South Island. The variability of the arrangement of the spines is just as great as in P. badia. The pullus is mostly brown and shining. The first two and a half whorls are always convex, never shouldered. The peritreme is continuous and brown. Young specimens have sometimes the body-whorl angled below the periphery, but no chordate carina is present. The size is very variable, ranging from 5 × 3 mm. with six whorls to 8½ × 5 mm. with seven whorls.

(5.) Lake Taupo (Stat. 6F—Dredged in 25 ft. to 420 ft.).—About two dozen specimens, showing the same characters as those of Stat. 6. The dimensions vary from 5½ × 3 mm. to 8½ × 5 mm., with six and seven whorls respectively.

(6.) Lake Taupo (Stat. 16F—Dredged in 280 ft. and 320 ft.,

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muddy bottom).—All the seven specimens are “dead shells,” therefore very fragile. They are shouldered, with traces of spines, covered with a dark-brown coating; no carina below the periphery. Dimensions range from 6½ × 4 mm. to 8½ × 5 mm.

(7.) Lake Taupo (Stat. 39—With weeds, from 20 ft. to 80 ft.).—There are seventeen specimens, of light-horn colour, and of an astonishing variability. Some call to mind the graceful, slender P. egenus, while others are more ventricose and short. Especially the elongated specimens show a very distinct angle on the body-whorl, arising from the junction of the outer lip with the whorl. Only a few are shouldered, but devoid of spines. The peritreme is dark-brown. The dimensions of four specimens are—4 × 2¾ mm.; 5½ × 2½ mm.; 6 × 3 mm.; 6 × 3½ mm. All adult specimens have six whorls.

(8.) Lake Taupo (Stat. 39F—With weeds, from 20 ft. to 80 ft.).—Four small specimens, covered with a grey coating, with six smooth convex whorls and a brown peritreme. They come very near P. antipodum, subsp. zelandiœ, but the whorls are more convex and the suture deeper. This is the most extreme form of salleana I have seen. The dimensions are—4 × 2¼ mm.; 4¼ × 2¼ mm.; 4½ × 2¼ mm.; 5 × 2½ mm.: the ratio of breadth to length varying from 1:1.6 to 1:2.

(9.) Lake Taupo (Stat. 40—With weeds, from 20 ft. to 80 ft.).—A large number of young specimens, most of which are distinctly angled below the periphery. Only two adult specimens, one smooth, one with spines. Colour, &c., the same as in examples from Stat. 39. The dimensions are 5 × 2½ mm. and 5 × 3 mm., with six whorls.

(10.) Lake Taupo (Stat. 40F—With weeds, from 20 ft. to 80 ft.).—Numerous young specimens, none adult, showing the same characters as those from Stat. 40, but they are covered by a green coating.

(11.) Lake Taupo (Stat. 47—Dredged in 400 ft.).—Four adult specimens, with a very thick black coating, very markedly shouldered, seven whorls, no spines, but there is an exceptionally strong carina; mouth snow-white. Dimensions, 7 × 4¼ mm.

(12.) Lake Waikaremoana (Stat. 3—Dredging in 50 ft. to 100 ft.).—Fifteen adult specimens, of a cinereous colour, with six whorls which are mostly shouldered and have rudimentary bristles; a few only have rounded smooth whorls. Peritreme light-brown. Dimensions range from 4½ × 2½ mm. to 6 × 3½ mm. These may be considered as typical forms.

(13.) Lake Waikaremoana (Stat. 17—Dredging in 800 ft.).—One specimen, a “dead shell,” with the last whorl broken off. It is thickly coated with calcareous substance, stained orange by oxide of iron. There are rudimentary spines visible on one

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whorl. Currents very likely brought this specimen to this considerable depth.

(14.) Lake Waikaremoana (Stat. 34—Dredging in 10 ft. to 20 ft.).—There are thirty-four adult shells, cinereous to black according to the amount of coating covering the shell. Most of them have six rounded smooth whorls, a few only are shouldered, none have spines. Peritreme brown. The dimensions vary from 5 × 2¾ mm. to 6½ × 3¾ mm. These also are typical examples.

(15.) Lake Manapouri (Stat. 15—From shallow water near the shore).—Two large adult specimens, both of which are of horn-colour, broadly shouldered, with distant brown spines on the carina, two or three arising from a common broad base. The larger example shows distinctly the slightly chordate carina below the row of spines on the last whorl, a character mentioned by P. Fischer. The other species, however, shows no trace of it; and it is, as I have pointed out elsewhere, not a constant but an extremely rare feature of salleana. The dimensions of the two shells are—8 × 5 mm. and 7 × 4 mm.

I have similar specimens from Lake Kanieri, kindly collected for me by Dr. Macandrew, of Hokitika, but they are more ventricose, and I assign them to P. corolla.

Potamopyrgus badia, Gould (1848).

Amnicola badia, Gould, Proc. Bost. Soc. Nat. Hist., vol. iii., 1848, p. 75.

(1.) Lake Wakatipu (Stat. 10—Dredged with weeds in 200 ft. to 300 ft.).—Seven shells of very light horn-colour, rather variable in size and shape. Only one, the largest, has spines; the others have the whorls convex, a few showing indications of a keel. They are very thin and fragile, the peritreme continuous in all, and light-brown. The largest shell measures 7 × 3½ mm., and it is very similar to the large specimens found in Lake Te Anau. The smallest shell, with six whorls, is 5 × 2½ mm.

(2.) Lake Wakatipu (Stat. 18—Dredged with weeds in 20 ft. to 100 ft.).—Ten shells, three of which are not adult, very variable in size, of light-horn colour, and very thin. Four have smooth, rounded whorls, two are slightly shouldered, and four are spinous. On the lower whorls the setæ are far apart, sometimes two to four bristles arising from a common base. All have six whorls, and the dimensions range from 5½ × 2½ mm., 6 × 3¼ mm., to 6½ × 3½ mm.

(3.) Lake Wakatipu (Stat. 6—From weeds fringing shore).—Seven shells of horn-colour, covered with a thin white coating, six convex whorls, suture impressed. Some examples are slightly shouldered on the upper whorls, with minute close-set short bristles. All are of about the same size—4¼ × 2¼ mm.

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Fam. Limnæidæ.

Sub-fam. Ancylinæ.
Genus Gundlachia, Pfeiffer (1849).

Zeitschrift f. Malak., vol. vi., 1849, p. 98.

Gundlachia lucasi, n. sp. Figs. 10, 11.

Lake Waikare (Stat. 30 and 30F—Netting in weeds).—Three specimens; two of them were collected alive. Shell obliquely conical, thin, semitransparent, horn-colour, covered by a blackish coating; apex inclined to the right, situated at the posterior third of the length; convex anteriorly, slightly concave on the posterior slope; a few concentric lines of growth. Aperture oval; peritreme sharp, extremely fragile. No septum, the shells being in the Ancylus stage of development only. Dimensions of two specimens—Length, 3 mm.; breadth, 2 mm.; height, 1 mm.: length, 4 mm.; breadth, 2¾ mm.; height, 1½ mm. The dentition is very similar to that of the Gundlachia sp. from the River Avon,* which, settles the generic position.

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Fig. 10

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Fig. 10a

This species stands nearest to G. tasmanica, T.-Woods. It is more rounded and elevated than the species from the River Avon. There is also one specimen of G. lucasi from Inglewood in my collection.

The occurrence of two species of Gundlachia in three different localities leaves no doubt that the genus is endemic, and accidental introduction out of the question.

Type in my collection.

I have great pleasure in uniting with the species the name of Mr. K. Lucas, who so ably and successfully collected the fauna of New Zealand lakes.

Sub-fam. Latiinæ.
Genus Latia, Gray (1850).
Latia neritoides, Gray (1850).

P.Z.S., 1849, p. 168 (1850).

Lake Waikare (Stat. 35—Dredged in 4 ft.; stony shore).—One small typical specimen, 5 mm. long.

Sub-fam. Limnæinæ.
Genus Amphipeplea, Nilsson (1822).

Nilsson, Hist. Moll. Suec., p. 58.

Amphipeplea arguta, Hutton (1885).

Trans. N.Z. Inst., vol. xvii., p. 54, pl. xii., fig. 1.

(1.) Lake Waikare (Stat. 19 and 19F—From reeds).—Fourteen

[Footnote] * Trans. N.Z. Inst., xxvi., pl. xiv., fig. 5.

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mostly young shells. Colour horny, columellar lip broadly reflexed. Dimensions—Shell: length, 7 mm.; breadth, 4 mm. Aperture: height, 5 mm.; breadth, 4 mm. Shell: length, 5½ mm.; breadth, 4 mm. Aperture: height, 4½ mm.; breadth, 3 mm.

(2.) Lake Taupo (Stat. 42—With weeds from 20 ft. to 80 ft.).—One specimen collected alive; yellowish-white, rather slender. The aperture more elongated than in the type. Shell: length, 5½ mm.; breadth, 3½ mm. Aperture: height, 4 mm.; breadth, 2½ mm.

(3.) Lake Wakatipu (Stat. 10—Dredged with weeds in 200 ft. to 300 ft.).—One specimen collected alive; nearly colourless, transparent, very thin and fragile, with broad columellar reflection; regular distinct incremental lines. The aperture is longer and narrower than in the type. Shell: length, 5¼ mm.; breadth, 3¼ mm. Aperture: height, 4½ mm.; breadth, 2½ mm.

(4.) Lake Wakatipu (Stat. 33—Dredged in 30 ft. to 60 ft.).—Two specimens collected alive. A slender form with elongated aperture, of horn-colour, with regular lines of growth, and the spire a little higher than typical. Shell: length, 5 mm.; breadth, 3 mm. Aperture: height, 3½ mm.; breadth, 2¼ mm. Shell: length, 4 mm.; breadth, 2½ mm. Aperture: height, 3½ mm.; breadth, 1¾ mm.

The Dentition.—Figs. 11–14 represent the most characteristic teeth of the radula of specimens from the four localities—fig. 11 from Lake Waikare, fig. 12 from Lake Taupo, fig. 13 from Stat. 10, and fig. 14 from Stat. 33, Lake Wakatipu. Compared with Hutton's description and figure of his species* a considerable variability, especially in the transitional teeth, is at once apparent. The central tooth shows mostly a second small denticle on the left side; the lateral teeth have all three cutting-points, but the entocone and mesocone may coalesce, forming only one cutting-point, as was evidently the case in the example

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Fig. 11

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Fig. 12

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Fig. 13

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Fig. 14

[Footnote] * Trans. N.Z. Inst., xvii., p. 54, pl. xii., fig. 10.

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figured by Hutton. The number of laterals and marginals is very variable, and the figures sufficiently show the different arrangements of the cutting-points on the transitional teeth.

Sub-fam. Planorbinæ
Genus Planorbis (Guett.), Geoffroy (1767).
Planorbis (Gyraulus) corinna, Gray (1850).

P.Z.S., 1849, p. 167 (1850).

Lake Waikare (Stat. 33—Obtained by netting in weeds).—One specimen only was found, which has three whorls and a diameter of 2½ mm.

Genus Isidora, Ehrenberg (1831).

Isidora tabulata, Gould, subsp. moesta, H. Adams (1861). P.Z.S., 1861, p. 144.

(1.) Lake Waikare (Stat. 19—From reeds).—One specimen only was obtained. It is of light-horn colour, very thin, covered with a greenish coating; there are four whorls, the last two distinctly shouldered and keeled. Columella excavated in the middle, fold distinct, reflection of columellar lip small; outer lip sharp, regularly arched. It is a little more slender than the type. Shell: length, 7 mm.; breadth, 4 mm. Aperture: height, 5 mm.; breadth, 2½ mm. Ratios: i. = 1: 1.75; ii. = 1: 2; iii. = 1: 1.4. (The ratios are the same as in the revision of Isidora.)

(2.) Lake Waikare (Stat. 28—From weeds in water from 1½ ft. to 2 ft.).—Two specimens of dark-brown colour, solid and large, keeled, the keel becoming obsolete on approaching the aperture; columella twisted. They differ but little from the type. Shell: length, 17½ mm.; breadth, 11 mm. Aperture: height, 11 mm.; breadth, 6 mm. Shell: length, 14 mm.; breadth, 9½ mm. Aperture: height, 10 mm.; breadth, 5 mm. Ratios: i. = 1: 1.6; ii. = 1: 1.8; iii. = 1: 1.6. i. = 1: 1.5; ii. = 1: 2; iii. = 1: 1.4. The accompanying fig. 15 shows some teeth of the radula, which need no explanation. The dentition of our forms of Isidora is so variable that I doubt whether it can be used as a help to separate the species. However, a considerable number of animals of each species has to be examined before this point can be settled definitively.

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Fig. 15

(3.) Lake Waikare (Stat. 28F—From weeds in water from 1½ ft. to 2 ft.).—Two “dead shells,” one young, the other nearly adult. They resemble those from the last station, but are a little more ventricose, and have the spire a little shorter. Shell:

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length, 15 mm.; breadth, 10 mm. Aperture: height, 10 mm.; breadth, 5.5 mm. Shell: length, 9 mm.; breadth, 6½ mm. Aperture: height, 6 mm.; breadth, 3½ mm. Ratios: i. = 1: 1.5; ii. = 1: 1.8; iii. = 1: 1.5. i. = 1: 1.5; ii. = 1: 1.7; iii. = 1: 1.5.

Isidora lirata, Tenison-Woods (1879).

P.L.S. N.S.W., vol. iii., 1879, p. 138, pl. xiii., fig. 6.

(1.) Lake Rotoiti (Stat. 12—From weeds in 6 ft.).—Six specimens, one only adult. The colour is light-horny, some specimens having a dark coating; the whorls are rounded, but slightly flattened below the suture, the spiral striæ are present but not very distinct. Aperture produced at the base, columella twisted. They are slightly more ventricose than the type. Shell: length, 12 mm.; breadth, 7 mm. Aperture: height, 8½ mm.; breadth, 4 mm. Shell: length, 10 mm.; breadth, 6 mm. Aperture: height, 7 mm.; breadth, 3½ mm. Shell: length, 8½ mm.; breadth, 5½ mm. Aperture: height, 5 mm.; breadth, 3 mm. Ratios: i. = 1: 1.7; ii. = 1: 2.1; iii. = 1: 1.4. i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.4. i. = 1: 1.5; ii. = 1: 1.7; iii. = 1: 1.7.

(2.) Lake Taupo (Stat. 7—Dredged with weeds in 75 ft.).—One specimen of cream colour, fragile; four whorls, shouldered down to the middle of the last whorl, carina with short bristles; shell indistinctly spirally striated; columella twisted, aperture much produced anteriorly. More ventricose than the type. Shell: length, 8 mm.; breadth, 5 mm. Aperture: height, 6 mm.; breadth, 3 mm. Ratios: i. = 1: 1.6; ii. = 1: 2; iii. = 1: 1.3.

(3.) Lake Taupo (Stat. 38—With weeds, from 80 ft.).—Many, mostly young specimens. They are of a dirty-white colour with a thin whitish coating. Whorls 4, rounded, sometimes flattened below the suture, beautifully regularly spirally striate. Columella twisted, aperture produced anteriorly. These I consider to be typical forms. Shell: length, 9½ mm.; breadth, 6 mm. Aperture: height, 7 mm.; breadth, 3 mm. Shell: length, 8½ mm.; breadth, 4¾ mm. Aperture: height, 6 mm.; breadth, 3 mm. Shell: length, 7½ mm.; breadth, 4½ mm. Aperture: height, 5 mm.; breadth, 2½ mm. Ratios: i. = 1: 1.6; ii. = 1: 2.3; iii. = 1: 1.4. i. = 1: 1.8; ii. = 1: 2; iii. = 1: 1.4. i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.6. Fig. 16 shows some teeth of the radula. A remarkable feature are the additional denticles on the outer upper side of the marginal teeth.

(4.) Lake Taupo (Stat. 38F—With weeds, from 80 ft.).—Many, mostly young shells. Very much like the specimens from

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Fig. 16

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Stat. 38, but the spiral striation is not so distinct, and the coating is thicker, of a greenish hue.

(5.) Lake Waikaremoana (Stat. 4—Dredging in 50 ft.).—Two “dead shells,” one adult with the apex broken off. They are rather large, of cream colour, with four rounded but slightly shouldered whorls; distinctly spirally lirate. Columella twisted, and aperture produced at base. Typical forms, though one much larger. Shell: length, 15½ mm.; breadth, 9 mm. Aperture: height, 10 mm.; breadth, 5 mm. Shell: length, 10½ mm.; breadth, 6 mm. Aperture: height, 7 mm.; breadth, 3 mm. Ratios: i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.6. i. = 1: 1.8; ii. = 1: 2.3; iii. = 1: 1.5.

(6.) Lake Waikaremoana (Stat. 5—Dredging in 50 ft.).—Six specimens, two of them quite young. The colour is light-horny, some shells with a ferrugineous coating. The whorls in some are rounded, in others shouldered and the keel ornamented with short bristles. In young specimens the spiral striation is quite distinct. Columella twisted, and aperture produced anteriorly. These again are typical forms. Dimensions of largest specimen: Shell: length, 13 mm.; breadth, 6¾ mm. Aperture: height, 8 mm.; breadth, 4 mm. Ratios: i. = 1: 1.9; ii. = 1: 2; iii. = 1: 1.6.

(7.) Lake Waikaremoana (Stat. 32—Dredging in 10 ft. to 20 ft.).—Four nearly adult and four young specimens. They are dirty-white, the longer examples with a light-brown coating. The four whorls are convex, very little flattened below the suture; spiral striation indistinct. These shells are very nearly typical. Dimensions of largest specimen:—Shell: length, 12 mm.; breadth, 6½ mm. Aperture: height, 8.5 mm.; breadth, 4 mm. Ratios: i. = 1: 1.8; ii. = 1: 2.1; iii. = 1: 1.4.

Synopsis of the Molluscan Fauna of the Six Lakes.

Lake Waikare.

Diplodon menziesi, Gray, subsp. rugata, Hutton.

Corneocyclas novozeelandica, Prime.

Potamopyrgus corolla, Gould.

" " " subsp. salleana, Fischer.

Gundlachia lucasi, Suter.

Latia neritoides, Gray.

Amphipeplea arguta, Hutton.

Planorbis corinna, Gray.

Isidora tabulata, Gould, subsp. moesta, H. Adams.

Lake Rotoiti.

Diplodon menziesi, Gray, subsp. hochstetteri, Dunker.

Sphærium novæ-zelandiœ, Deshayes.

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Potamopyrgus corolla, Gould, subsp. salleana, Fischer.

Isidora lirata, Tenison-Woods.

Lake Taupo.

Diplodon menziesi, Gray.

Sphærium novæ-zelandiœ, Deshayes.

Corneocyclas hodgkini, Suter.

Potamopyrgus corolla, Gould.

" " " subsp. salleana, Fischer.

Amphipeplea arguta, Hutton.

Isidora lirata, Tenison-Woods.

Lake Waikaremoana.

Diplodon menziesi, Gray.

Sphærium novæ-zelandiœ, Deshayes.

Corneocyclas hodgkini, Suter.

Potamopyrgus corolla, Gould, subsp. salleana, Fischer.

Isidora lirata, Tenison-Woods.

Lake Wakatipu.

Diplodon lessoni, Kuster.

Corneocyclas novozeelandica, Prime.

Potamopyrgus badia, Gould.

Amphipeplea arguta, Hutton.

Lake Manapouri.

Diplodon menziesi, Gray, subsp. lucasi, Suter.

Corneocyclas novozeelandica, Prime.

Potamopyrgus corolla, Gould, subsp. salleana, Fischer.

" badia, Gould.

Bathymetrical Distribution of the Mollusca.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

—— Lake. Depth in Feet.
Diplodon menziesi, Gray Taupo 100
" " Waikaremoana 10–50
" " subsp. hochstetteri, Dunker Rotoiti 12
" " subsp. hochstetteri, Dunker Taupo 10–30
" " subsp. rugata, Hutton Waikare 2
" " subsp. lucasi, Suter Manapouri 60
Diplodon lessoni, Kuster Wakatipu 10–30
Sphærium novæ-zelandiæ, Deshayes Rotoiti 6
" " Taupo 20–100
" " Waikaremoana 10–20
Corneocyclas novo-zeelandica, Prime Waikare 2
" " Wakatipu 10–100
" " Manapouri Shallow
Corneocyclas hodgkim, Suter Taupo 280–320
" " Waikaremoana 800
Potamopyrgus corolla, Gould Waikare Shallow
" Taupo 280–320
" " subsp. salleana, Fischer Waikare Shallow
" " subsp. salleana, Fischer Rotoiti 6
" " subsp. salleana, Fischer Taupo 20–420
" " subsp. salleana, Fischer Waikaremoana 10–100
" " subsp. salleana, Fischer (dead) " 800
" " subsp. salleana, Fischer Manpouri Shallow
Potamopyrgus badia, Gould Wakatipu 20–300
" " Manapouri Shallow
Gundlachia lucasi, Suter Waikare "
Latia neritoides, Gray " 4
Amphipeplea arguta, Hutton " Shallow
" " Taupo 20–80
" " Wakatipu 20–300
Planorbis corinna, Gray Waikare Shallow
Isidora tabulata, Gould, subsp. moesta, H. Adams " 2
Isidora lirata, Tenison-Woods Rotoiti 6
" " Taupo 75–80
" " Waikaremoana 10–50
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Summary.

The Mollusca collected by Messrs. Lucas and Hodgkin in the six lakes of New Zealand belong to nine genera, and these are represented by twelve species and five subspecies. As new we find one subspecies of Diplodon menziesi, one species of Corneocyclas, and one species of Gundlachia. Am interesting addition to our fauna is Diplodonta lessoni, Küster.

From Lake Rotoiti no specimens of Potamopyrgus badia, Gould, and Melanopsis trifasciata, Gray, were obtained, but it is almost certain that Potamopyrgus corolla, subsp. salleana, was taken for P. badia, and I never have seen an example of Melanopsis trifasciata from Lake Rotoiti, though I tried hard to get some. In the Lake of Tiberiade, in Palestine, Melanopsis has been found at a depth of about 150 ft.

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From Lake Wakatipu Planorbis corinna and Isidora antipodea were not represented.

All the Mollusca living in deeper water have much lighter colours, and the test is much thinner and more fragile. With one exception (Corneocyclas hodgkini) there is no real deep-lake fauna in these lakes, such as it is known from the subalpine lakes in Switzerland, &c., and this may partly be explained by the poverty of our lakes in molluscan life. Limnæa is absent, its place being taken by Amphipeplea, and it is interesting to find this genus represented by one species only.

The littoral fauna, according to Forel's investigations,* extends to 50–75 ft., and it is therefore evident that many of our known species can live in deeper water without undergoing any great structural change. Generally Unionidœ are not found in very deep water. However, Anodonta ponderosa, Pfr., was obtained in 33 ft. in Lake Tschaldyr, in Armenia, by Dr. Brandt, and five species of Unio were dredged in 150–300 ft. in Lake Tiberiade, in Palestine, by Lortet.

Sphœrium and Isidora have, as far as I know, not been known to live in deeper water, and of Potamopyrgus it is for the first time we get any accurate knowledge of the depths of water in which it may be found living.

The deep-lake molluscan fauna of New Zealand, as far as Messrs. Lucas and Hodgkin's investigations go, may be considered to be composed of the following species:—

(1.) Diplodon menziesi, Gray.

(2.) " " subsp. lucasi, Suter.

(3.) Sphærium novæ-zelandiœ, Deshayes.

(4.) Corneocyclas novozeelandica, Prime.

(5.) " hodgkini, Suter.

(6.) Potamopyrgus corolla, Gould.

(7.) " " subsp. salleana, Fischer.

(8.) Potamopyrgus badia, Gould.

(9.) Amphipeplea arguta, Hutton.

(10.) Isidora lirata, Tenison-Woods.

[Footnote] * Dr. F. A. Forel, “La Faune profonde des Lacs Suisses,” 1885.