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Volume 37, 1904
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Art. XVI.—Revision of the New Zealand Species of the Genus Isidora, with Description of a New Subspecies.

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

The first short list of species we find in von Marten's “Critical List” (1873), p. 15, consisting of three species: Physa variabilis, Gray; P. tabulata, Gould; and Limnæa (?) wilsoni, Tryon (a sinistral shell). The next list, in Hutton's Manual, is more extensive, comprising ten species: Physa wilsoni, Tryon; P. antipodea, Sow.; P. gibbosa, Gould; P. guyonensis,

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T.-Woods; novæ-zelandiœ, Sow.; P. tabulata, Gould; P. variabilis, Gray; P. moesta, Ad.; P. lirata, T.-Woods; and P. cumingii, Ad. In vol. vii., P.L.S. N.S.W., Captain Hutton published a list of the fresh-water shells of New Zealand, in which the species of the genus were reduced to four—Aplexa antipoda, Sow.; A. tabulata, Gould; A. variabilis, Gray (= gibbosa, Sow. not Gould, guyonensis, T.-Woods, hochstetteri, Dkr.); and A. moesta, Ad. In 1885 Captain Hutton gave a list of the Limnæidæ in these Transactions, vol. xvii., enumerating Bulinus antipodeus, Sow.; B. variabihs, Gray (= gibbosus, Hutt. non Gould, novæ-zealandiæ, Sow., guyonensis, T.-Woods); B. tabulatus, Gould; and B. moesta, Adams (= lirata, T.-Woods), giving a description and figure of the dentition of the latter. The following species were omitted as not really inhabiting New Zealand: Limnæa wilsoni, Tryon, like Physa pyramidata, Sow., from Australia; Physa gibbosa, Gould, inhabiting New South Wales; and Physa cumingi, Ad., inhabiting Queensland.

In Fischer's Manual, p. 257, we find only two species recorded: Physa guyonensis and P. moesta. With my friend Mr. Charles Hedley, of Sydney, I published in 1893 a “Reference List of the New Zealand Land and Fresh-water Shells,” in which, for the species of Isidora, Hutton's latest classification was chiefly adopted, reducing, however, the species to three: Bulinus antipodeus, Sow.; B. variabilis, Gray (= guyonensis, T.-Woods, novœ-zelandiœ, Sow.); and B. tabulatus, Gould (= moesta, Adams, lirata, T.-Woods). Mr. Hedley added the following species, which for want of literature had escaped the notice of New Zealand conchologists: B. novœ-seelandiœ, Clessin; tenisoni, Clessin; coromandelicus, Dkr.; and hochstetteri, Dkr.

The following year I published, at the request of Mr. H. Crosse, a somewhat more extensive list in the Journ. de Conch., vol. xli., adhering still to three species of Isidora, and reducing Clessin's and Dunker's species to synonyms, as follows: Bullinus variabilis, Gray (= guyonensis, T.-Woods, novœ-zelandiœ, Sow., gibbosus, Hutt. non Gould, novœ-seelandiœ, Clessin); B. tabulatus, Gould (= moesta, H. Ad., lirata, T.-Woods, coromandelicus, Dkr., hochstetteri, Dkr.); and B. antipodeus, Sow.

I have studied now the description and copy of figure, kindly supplied to me by Mr. Hedley, of Physa novœseelandiœ, Clessin, and find it to be identical with Physa lessoni, E. A. Smith, an Australian shell, and it has therefore to be omitted from the list of New Zealand shells. Physa tenisoni, Clessin, is according to the figure a Limnœa, being dextral. Physa hochstetteri, Dunker, was mentioned by Hutton as a synonym of Aplexa variabilis, Gray (antea), but was never mentioned again in his later publications.

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When working out the Mollusca collected by Mr. K. Lucas in New Zealand lakes, I had the same experience with Isidora as with Potamopyrgus: the lumping of species had been carried on too far. I do not wish to exonerate myself from blame, and I freely confess that never before have I made a careful study of our species of Isidora, as their great variability makes it extremely difficult to decide the limit of species and subspecies. A good collection of specimens from various localities, besides plenty of time and patience, is necessary for the successful study of these fresh-water molluscs. Specimens from over twenty localities were used to write the present revision, and I hope that it will form a sound basis to work upon.

Physa variabilis was the first species described by Gray (in “Dieffenbach's Travels,” vol. ii. (1843), p. 248). The very short diagnosis, unaccompanied by a figure, has in my opinion been the curse of New Zealand conchologists. From the many species judged to be synonyms of this unfortunate variabilis it can be gathered that no one ever knew what Gray's species is—perhaps not even Gray himself, for his diagnosis fits nearly all our species. So it has become a regular olla podrida: all the forms that did not fall under a recognised species were simply labelled “variabilis, Gray.” I have come to the conclusion that as long as we retain this species there is no possibility of classifying our various forms of Isidora correctly, and I reject it as insufficiently described, unfigured, and embracing perhaps several distinct species.

Genus Isidora, Ehrenberg (1831).

Synonyms: Diastropha, Gray (1840); Ameria, H. Adams (1861); Glyptophysa, Crosse (1872); Pyrgophysa, Crosse (1879); Physastra, Tapparone Canefri (1883).

Animal without the produced and reflected mantle-lobes of Physa; radula Limnæidian, approaching Planorbis rather than Limnœa; central tooth bicuspid, cusps rather blunt, base square; laterals tricuspid; marginals serrate. Laterals about 6–10, marginals about 25–33. Number of rows varying between 140 and 220.

Shell sinistral, resembling that of Physa, acuminated or gibbous, smooth or keeled; texture somewhat thick, covered with a deciduous epidermis; columella strong, often reflected, umbilicus sometimes very wide and deep.

Distribution: Australia, Tasmania, New Zealand, New Guinea, New Caledonia, Fiji, Tonga, Africa (north, north-east, west, and south), southern France, Spain, and all countries bordering the Mediterranean.

Ameria was proposed for Physœ with keeled whorls. The

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distinction is untenable. Every gradation of keeling is observable in the Australian Isidorœ (Rev. A. H. Cooke).

Isidora tabulata, Gould (1848), sp.

Physa tabulata, Gould, Proc. Boston Soc. Nat. Hist., vol. ii. (1848), p. 214; U.S. Expl. Exp., vol. xii., p. 116, figs. 136 a, b. Physa tabulata, v. Martens, Crit. List N.Z. Moll. (1873), p. 15. Physa tabulata, Hutton, Man. N.Z. Moll. (1880), p. 30. Aplexa tabulata, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus tabulatus, Hutton, Trans. N.Z. Inst., vol. xvii. (1885), p. 57. Physa tabulata, A. H. Cooke, P.Z.S. (1889), pp. 139, 140, fig. 4 (radula). Bulinus tabulatus, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii. (1893), p. 627. Bullinus tabulatus, Suter, Journ. de Conch., vol. xli. (1894), p. 233.

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Fig. 1

The diagnosis is to be found in Hutton's Manual. Fig. 1 represents the species after a copy from Reeve (Conch. Icon., vol. xix., Physa, fig. 17b), kindly supplied with several others by Mr. Hedley. Taken from the figure the dimensions are—Shell: length, 22 mm.; breadth, 16 mm. Aperture: length, 12 mm.; breadth, 8 mm. I think it to be a most useful thing to establish the following rationis to help in separating the various forms: i. Ratio between breadth and length of shell = 1: 1.4; ii. ratio between breadth and length of aperture = 1: 1.5; iii. ratio between length of aperture and length of shell = 1: 1.8. Hereafter I shall designate these rationis simply by i., ii., iii.

Hob. A mountain-stream, Bay of Islands (Drayton).

Type in the U.S. Nat. Museum, Washington.

I have not seen this species.

Isidora tabulata, Gould, subsp. moesta, H. Adams (1861), subsp. Physa moesta, H. Adams, P.Z.S. (1861), p. 144. Physa coromandelica, Dunker, Malac. Blätter (1862), p. 150. Physa moesta, Hutton, Man. N.Z. Moll. (1880), p. 31. Aplexa moesta, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus moesta, Hutton, Trans. N.Z. Inst., vol. xvii., p. 57, pl. xii., fig. 12 (dentition). Bulinus moesta et coromandelica, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., pp. 627, 628. Bullinus moesta et coromandelica, Suter, Journ. de Conch., vol. xli., p. 233.

The very short diagnosis is fortunately supplemented by a figure in Reeve's Conch. Icon., fig. 32, the outlines of which I here reproduce (fig. 2). The dimensions, taken from the figure, are—Shell: length, 17 mm.; breadth, 11 mm. Aperture: length, 10 mm.; breadth, 5 mm. The proportions are: i. = 1: 1.5; ii. = 1: 2; iii. = 1: 1.7.

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Fig. 2.

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I have examined and measured specimens in my collection from the following localities:—

(1.) Ditch near Lake Takapuna, Auckland. The specimens are fuscous, with a ferrugineous coating, shouldered, larger and more slender than the type. Two specimens measured gave length of shell 15 mm. and 17 mm., breadth 9 mm.; and the mean proportions were found to be—i. = 1: 1.8; ii. = 1: 2; iii. = 1: 1.7.

(2.) From Lake Takapuna, Auckland. Two specimens, dark-brown, strongly carinated, larger and a little less ventricose than the type. Shell: length, 12–15½ mm.; breadth, 7–9 mm. Mean rationis—i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.5.

I first tried to uphold I. coromandelica, Dunker, as a separate subspecies of I. tabulata, as the specimens of the above three localities approach the ratio between breadth and length of shell of I. coromandelica, which is 1: 2, but I soon found out that all intermediate forms, from the elongated coromandelica to the more ventricose moesta, are met with, and, as there seems to be no other character available to distingusih the two, I thought it advisable to make the former a synonym of the latter.

(3.) Wanganui (no exact locality). One adult and two not quite full-grown specimens were measured. The adult had—length, 17 mm.; breadth, 10 mm. All specimens are shouldered. The mean proportions are—i. = 1: 1.6; ii. = 1: 2.1; iii. = 1: 1.4.

(4.) Fresh-water stream, Parua Bay, Whangarei. All specimens are blackish-brown, two are distinctly shouldered, the other has smooth whorls. The columellar fold is very distinct. Three shells showed the length to vary from 9–15 mm., the breadth from 5½–9½ mm. The mean proportions are—1 = 1: 1.7; ii. = 1: 1.9; iii. = 1: 1.6.

(5.) Waikato River, near Huntly. Shells of good size, chestnut-colour, some with a ferrugineous coating; young specimens are strongly carinated, in adult specimens the carina is reduced to a slight angulation on the last whorl. Columella strongly twisted. Four shells were measured, the length being 12–15 mm.; breadth, 8–11 mm. The mean proportions were—i. = 1: 1.4; ii. = 1: 1.9; iii. = 1: 1.5.

(6.) Chatham Islands. One specimen only, of yellowish-brown colour, with four shouldered whorls. This is a slender form. Length, 8 mm.; breadth, 4½ mm. Rationis—1 = 1: 1.8; ii. = 1: 2; iii. = 1: 1.6.

The result of measuring twenty-eight specimens is the following: Ratio i.—variability, 1: 1.4 to 1: 1.8; mean, 1: 1.65. Ratio ii.—variability, 1: 1.9 to 1: 2.3; mean, 1: 2. Ratio iii.—variability, 1: 1.4 to 1: 1.7; mean, 1: 1.5. It shows that the shells of this subspecies are a little more slender and the spire

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is somewhat higher in proportion to the length of the aperture than in the type specimen figured.

Type in the British Museum (?).

Isidora hochstetteri, Dunker (1862), sp.

Physa hochstetteri, Dunker, Malac. Blatter, vol. ix. (1862), p. 150. Physa guyonensis, T.-Woods, P.L.S. N.S.W., vol. iii. (1879), p. 138, pl. xiii., fig. 4. Physa guyonensis, Hutton, Man. N.Z. Moll., p. 30. Physa guyonensis et hochstetteri, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus guyonensis et hochstetteri, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., pp. 627, 628. Bullinus guyonensis et hochstetteri, Suter, Journ. de Conch., vol. xli., pp. 232, 233.

The diagnosis of guyonensis is in Hutton's Manual. The accompanying fig. 3 is drawn from a tracing of the figure given by Tenison-Woods. Captain Hutton mentions (Manual) that Dr. Dohrn determined specimens from the same locality (Lake Guyon) as P. hochstetteri, Dkr. The diagnosis agrees in the main points with that of T.-Woods, and Dunker particularly mentions the deep suture and the amplitude of the body-whorl. I do not hesitate to accept the determination of the distinguished conchologist, Dr. Dohrn. The dimensions of P. hochstetteri are—Height, 17 mm.; breadth, 9 mm. For P. guyonensis the dimensions given by T.-Woods are—Height of shell, 15 mm.; breadth, 7½ mm.: aperture—height, 9 mm.; breadth, 5 mm. I have not seen specimens from Lake Guyon, but I have shells from Lake Nga-tu, Kaitaia, which I consider to belong to this species, although they are somewhat shorter and more ventricose than the type; otherwise they agree with the diagnosis. Especially the deep suture is characteristic, no other of our species showing this character in such a marked degree. All my examples are “dead shells” of a light-brown colour.

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Fig. 3.

For I. guyonensis the rationis are—i. = 1: 2; ii. = 1: 1.8; iii. = 1: 1.7. For hochstetteri—i. = 1: 1.9. I measured four of my specimens. The length of the shell varies from 13½–14½ mm., the breadth from 8–9 mm. Aperture—length, 8–9 mm.; breadth, 4–5 mm. The mean proportions are—i. = 1: 1.6; ii. = 1: 1.9; iii. = 1: 1.6.

Hab. The only localities known to me are Lake Guyon, Nelson, and Lake Nga-tu, in the high north.

Type in the K.K. Hofmuseum, Vienna (?).

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Isidora novæ-zelandiœ, Sowerby (1873), sp.

Physa novœ-zelandiœ, Sowerby, Reeve, Conch. Icon., vol. xix., Physa, sp. 29 (1873). Physa novœ-zelandiœ, Hutton, Man. N.Z. Moll., p. 30. Bulinus novœ-zelandiœ, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., p. 627. Bullinus novœ-zelandiœ, Suter, Journ. de Conch., vol. xli., p. 232.

The diagnosis of this species is also contained in Hutton's Manual, and I reproduce here a figure (4) from a tracing of fig. 29b in Conch. Icon. Taken from the figure the dimensions are—Shell: length, 20½ mm.; breadth, 12¼ mm. Aperture: length, 15 mm.; breadth, 6 mm. Proportions—i. = 1: 1.7; ii. = 1: 2.5; iii. = 1: 1.4.

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Fig. 4.

I have only two specimens from the North Island, exact locality unknown. One adult specimen has smooth whorls, the other, not full-grown, is shouldered. The dimensions are—Shell: length, 17 mm.; breadth, 12 mm. Aperture: length, 14 mm.; breadth, 6½ mm. Shell: length, 14 mm.; breadth, 9½ mm. Aperture: length, 10 mm.; breadth, 4½ mm. The mean proportions—i. = 1: 1.5; ii. = 1: 2.2; iii. = 1: 1.3. The adult specimen is of chestnut-colour, the young horny-olive. The spire is shorter and the last whorl not quite so broad posteriorly, nor so flat at the periphery, as the figure of the type indicates.

Type in Mr. Sowerby's cabinet (?).

Isidora antipodea, Sowerby (1873), sp.

Physa antipodea, Sowerby, Reeve, Conch. Icon., vol. xix., Physa, sp. 37 (1873). Physa antipodea, Hutton, Man. N.Z. Moll., p. 30. Aplexa antipoda, Hutton, P.L.S. N.S.W., vol. vii., p. 67. Bulinus antipodeus, Hutton, Trans. N.Z. Inst., vol. xvii., p. 56. Bulinus antipodeus, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., p. 627. Bullinus antipodeus, Suter, Journ. de Conch., vol. xli., p. 233.

Diagnosis in Hutton's Manual. I reproduce here (fig. 5) the outlines of the species after Reeve. This seems, as far as our scanty knowledge goes, to be the only one of our species that has constantly smooth whorls. The dimensions taken from the figure are—Shell: length, 22 mm.; breadth, 12 mm. Aperture: length, 13 mm.; breadth, 6½ mm. Rationis—i. = 1: 1.8; ii. = 1: 2; iii. = 1: 1.7.

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Fig. 5.

This species is represented in my collection by two specimens from Lake Wakatipu, and the dimensions are—Shell: length, 17 mm.; breadth, 10½ mm. Aperture: length, 11 mm.; breadth, 5½ mm. Shell: length, 18½ mm.; breadth, 11 mm. Aperture: length, 12 mm.; breadth,

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6 mm. Mean rationis—i. = 1: 1.7; ii. = 1: 2; iii. = 1: 1.5. These specimens are slightly more ventricose and have the aperture in proportion shorter than the type.

Hab. Lake Hayes, Otago; near Napier; Lake Wakatipu.

Type in Mr. Sowerby's cabinet (?).

Isidora lirata, Tenison-Woods (1879), sp.

Physa lirata, T.-Woods, P.L.S. N.S.W., vol. iii. (1879), p. 138, pl. xiii., fig. 6. Physa lirata, Hutton, Man. N.Z. Moll., p. 31; Trans. N.Z. Inst., vol. xvii., p. 57. Bulinus liratus, Hedley and Suter, P.L.S. N.S.W. (2), vol. vii., p. 627. Bullinus liratus, Suter, Journ. de Conch., vol. xli., p. 233.

The diagnosis is also in Hutton's Manual, and the accompanying fig. 6 is reproduced from T.-Wood's figure. Fig. 6a shows a few teeth of the radula: the rhachidian tooth is bicuspid, the laterals tricuspid, the following transition teeth with four and more denticles, and the marginals are elongate and serrate.

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Fig. 6.

This is one of the best-characterized species; the fine spiral lirae and the anteriorly produced lip distinguish it at once from all the other New Zealand species. The dimensions given by T.-Woods are—Shell: length, 10 mm.; breadth, 5 mm. Aperture: length, 5 mm.; breadth, 3 mm. The proportions are—i. = 1: 2; ii. = 1: 1.7; iii. = 1: 2: but taken from the figure we get—i. = 1: 1.9; ii. = 1: 2.2; iii. = 1: 1.5.

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Fig. 6a.

In my collection the species is represented from twelve localities: Rivers Heathcote and Avon, creek in St. Albans, pond in Fendalton, all near Christchurch; Wellington; Greymouth; Pelorus River; pond near Lake St. John; Toko; Lakes Virginia and Westmere, near Wanganui; and North Island, exact locality unknown. The specimens vary a great deal in size and proportions, but the main features mentioned above are always present. The colour is usually light-horny, the whorls are sometimes smooth but mostly strongly carinated, and the carina usually adorned with short light-brown bristles, a character only met with in this species.

I measured altogether thirty-one specimens and found the rationis to vary—i., from 1: 1.6 to 1: 1.9; ii., from 1: 1.6 to 1: 2.4; iii., from 1: 1.3 to 1: 1.7. The means are as follows—i. = 1: 1.7; ii. = 1: 1.9; iii. = 1: 1.5.

Type where ?

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Isidora lirata, T. Woods, subsp. conferta, n. subsp.

Shell globosely ovate, sinistral, corneous-translucent, thin, almost imperforate, the columellar reflexion leaving only a narrow chink. The distant lines of growth are rather regular, especially on the upper whorls, and under the lens fine regular and close spiral liræ are visible. The colour varies from very light horny to light olive-brown. The spire is short, about one-third the length of the shell. The pullus is acuminate, of darker colour, consisting of two whorls with fine incremental striation. There are four whorls, either strongly shouldered or having only a posterior angle, which usually gets lost on the body-whorl; the latter is forming the greater part of the shell. The base is convex, the suture impressed. Aperture vertical, elongately oval, acuminate above and produced anteriorly. The outer lip is regularly rounded, sharp, thin; the inner lip is twisted, forming a distinct fold near the axis of the shell; not much reflexed. Fig. 7 represents a distinctly shouldered form, and fig. 8 with only a slight angulation on the whorls.

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Fig. 7

This subspecies is distinguished from the species by its ventricose form and the much broader aperture, approaching T. tabulata, Gould. I have specimens from two localities:—

(1.) From swamps near Otorohanga, King-country. These are strongly keeled (fig. 7). Three specimens were measured—Shell: length, 11 mm.; breadth, 7 mm. Aperture: length, 7 mm.; breadth, 4 mm. Shell: length, 9½ mm.; breadth, 6½ mm. Aperture: length, 6½ mm.; breadth, 3½ mm. Shell: length, 9½ mm.; breadth, 6 mm. Aperture: length, 6 mm.; breadth, 3¼ mm. The mean rationis are—i. = 1: 1.6; ii. = 1: 1.7; iii. = 1: 1.6.

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Fig. 8.

(2.) From Wairau River, south of Birch Hill Station, Nelson. These specimens are much lighter in colour, the upper whorls slightly angled (fig. 8). Three specimens were measured—Shell: length, 11–12 mm.; breadth, 7–7½ mm. Aperture: length, 8–8½ mm.; breadth, 4½ mm. The mean proportions are—i. = 1: 1.6; ii. = 1: 1.9; iii. = 1: 1.4. The means for the two localities are—i. = 1: 1.6; ii. = 1: 1.8; iii. = 1: 1.5.

Type in my collection.

To repeat, the following species are omitted:—

(1.) Physa variabilis, Gray, insufficiently described and unfigured.

(2.) Physa gibbosa, Gould, inhabits Australia.

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(3.) Physa cumingi, H. Ad., inhabits Australia.

(4.) Physa wilsoni, Tryon, inhabits Australia; perhaps pyramidata, Sow.

(5.) Physa novœseelandiœ, Clessin = P. lessoni, E. A. Smith, Australia.