Art. XX.—Notes on New Zealand Mollusca: No. 1, Descriptions of Three New Species of Polyplacophora, and of Damoniella alpha.
[Read before the Wellington Philosophical Society, 22nd October, 1919; received by Editor, 21st December, 1920; issued separately, 4th July, 1921.]
In this paper four new species of Mollusca are described, the types of which are in the Dominion Museum, three of them belonging to the order Polyplacophora, or chitons. Two were obtained within a short distance of Wellington, but repeated search has failed to discover further specimens. Damoniella alpha is, unfortunately, the only specimen so far obtained; it was discovered by Dr. J. A. Thomson in the fossil-beds at Blue Cliffs, Otaio River. It adds a new genus as well as a new species to the New Zealand Tertiary fauna.
The excellent drawings from which the accompanying plate was prepared were done by Miss J. K. Allan, of Sydney, and hearty thanks are due to her for the careful, accurate work bestowed upon them.
Plaxiphora (Maorichiton) Iredale (1).*
Plaxiphora (Maorichiton) lyallensis n. sp. (Plate XXXVIII, figs 7–8.)
Lyall Bay, Cook Strait, N.Z.
Shell oval, flatly arched, side slopes straight, surface dull. Anterior valve with eight radial ribs, rendered slightly nodulous by the irregularly spaced growth-lines; the spaces between the radials appear smooth, but a strong pocket-lens shows traces of V-like sculpture. Median valves squarish, not beaked, nearly smooth; lateral areas raised, marked off by a strong semi-nodulous rib, the central portion covered with very fine V-like sculpture; the jugal areas with traces of microscopic striae and pitting; the pleural areas with a few horizontal wrinkles in a shallow groove anterior to the lateral rib; this groove is most distinct in valves 4 to 6. Posterior valve small, mucro terminal, slightly upturned, pleural areas bounded by a strong marginal rib, no sculpture. Interior deep blue-green, sutural plates white, sinus rather broad, convex in centre with a central dark-brown spot and a yellow tinge on either side of it. The anterior valve has eight slits, the edges of which are thickened and upturned, the insertion plates lightly grooved. The median valves also have the insertion plates grooved, and one slit. The posterior valve has a thickened rib-like insertion plate.
Colour: Ground-colour greenish-brown, irregularly barred with cream, the sixth valve cream with irregular zigzags of the ground-colour, the anterior valve uniform brown.
[Footnote] *This and other numbers enclosed in parentheses refer to the list of literature at end of paper.
Fig. 1.—Lorica haurakiensis n. sp.
Fig. 2.—Lorica haurakiensis n. sp. : profile.
Fig. 3.—Lorica haurakiensis n. sp. : second valve.
Fig. 4.—Lorica volvox (Reeve).
Fig. 5.—Lorica volvox (Reeve): profile.
Fig. 6.—Lorica volvox (Reeve): second valve.
Fig. 7.—Plaxiphora (Maorichiton) lyallensis n. sp.
Fig. 8.—Plaxiphora (Maorichiton) lyallensis n. sp. : profile.
Fig. 9.—Rhyssoplax oliveri n. sp. : girdle-scales.
Fig. 10.—Rhyssoplax oliveri n. sp. : girdle-scales.
Fig. 11.—Rhyssoplax oliveri n. sp. : profile.
Fig. 12.—Damoniella alpha n. sp.
Girdle moderately broad, with a marginal fringe of soft short bristles, and about twenty tufts and pores adjoining the valves; when alive it was a greenish colour.
Measurements: Length, 35 mm.; breadth, 20 mm.; but it would probably have been at least 5 mm. longer and broader in life.
Material: The holotype, in the Dominion Museum.
Remarks.—This specimen was obtained accidentally when gathering Ulva-covered pieces of rock; a tuft came away readily, and I found it was on this chiton, which it had completely hidden. Having no idea is was a new species, it was not measured while alive, nor was the radula preserved. In spite of repeated searches in the same place, no further specimens have been obtained. It belongs to the group of Plaxiphora which has been placed by Iredale in the subgenus Maorichiton, with Chiton caelata Reeve as the type.
Lorica H. and A. Adams' (2).
Lorica haurakiensis n. sp. (Plate XXXVIII, figs. 1–3.)
Lorica volvox Suter (non Reeve) (3).
Off Kawau Island, Hauraki Gulf, N.Z.; 20 fathoms.
Shell ovately oblong, steeply elevated, dorsal ridge acute, side slopes very slightly convex. Anterior valve erect, lightly curved forward, with fourteen ‘irregularly spaced radial ribs,’ smooth for about two-thirds their length, but bearing near the girdle from four to six low, steeply rounded nodules; the interstices show faint concentric growth-line; posterior angles of the apex finely vertically ribbed. Median valves : The first of these is considerably larger than the others the jugal area sculptured with oblique radial ribs which form inverted “V” up it (Plate XXXVIII, fig. 3); pleural areas finely horizontally ribbed. In valves 3 to 8 the horizontal ribbing is continued across the jugal tract The number of ribs varies with the age of the shell; the holotype has nineteen horizontal ribs, the interstices rather wider and perfectly smooth. The lateral areas raised, somewhat variable, some having two or three more-or-less-decided radial riblets, but they may be obsolete on one or more of these areas. A few low, steeply rounded nodules are rather irregularly scattered over the riblets. Posterior edges of valves denticulate, and showing traces of fine vertical striae at the apex. The concentric growth-lines are clearly visible. Posterior valve the smallest, horizontally ribbed, bounded by a strong slightly upstanding rib, bearing a few nodules. In some specimens there are traces of fine vertical riblets on the posterior angle. The mucro is terminal. The valve rather deeply grooved posteriorly.
Girdle medium width, closely set with smooth convex scales, which vary slightly in size. There are no tufts of bristles; the posterior slit extends the whole width of the girdle. Unfortunately this is not shown in fig. 1.
Colour reddish-brown with a fairly broad creamy-yellow bar along the centre of the shell. The girdle about the same colour, with darker transverse bars. Individual specimens appear to vary somewhat in colour. Interior reddish, sutural plates almost white, sinus very narrow, rather shallow. Anterior valve with about eight slits, median valves one slit. Owing to the scarcity of specimens it has not been possible to disarticulate one.
Measurements: Holotype—length, 30 mm.; breadth, 20 mm. The largest paratype about 40 mm. by 30 mm.; but it is rather contracted, and therefore difficult to measure accurately.
Material : The holotype, presented by Mr. A. E. Brookes to the Dominion Museum, and four paratypes.
Remarks.—Hitherto this species has been confused with Lorica volvox (Reeve), though the resemblance is really only superficial, as, careful comparison shows several decided differences between the two species. A study of figs. 2 and 5 on the accompanying plate reveals a striking difference in the general outline of the shells, Lorica haurakiensis having a much steeper outline than Lorica volvox (Reeve). Figs. 3 and 6 show the remarkable difference in sculpture of the second valve of each species, fig. 3 (L. haurakiensis) exhibiting no trace of the nodulous sculpture so characteristic of L. volvox (Reeve) (fig. 6) on the jugal tract. Also, the lateral areas of L. haurakiensis are very much less nodulous than in L. volvox. The pleural areas of the species differ in that L. haurakiensis has the interstices of the longitudinal ribs smooth, while in L. volvox the whole surface is rendered semi-nodulous by low heavy transverse corrugations.
There are also differences in the girdle characters, the new species being characterized by small close-set scales, and by the entire absence of the tufts of transparent bristles, which are numerous on L. volvox.
History.—In 1872 Hutton (4) described Chiton rudis from a specimen in the Colonial Museum, and stated “Locality unknown.” That specimen has since been identified at Chiton volvox Reeve (1847), now placed in the genus Lorica. It is specifically inseparable from specimens presented by Mr. C. Hedley.
When inspecting the concrete sinker of the buoy off Whale Rock, Bay of Islands, a few years ago, Captain Bollons obtained two or three specimens, in about 20 fathoms, which the late Mr. Suter identified as Lorica volvox (Reeve) (3). Since then Mr. A. E. Brookes has obtained three more specimens off Kawau Island, Hauraki Gulf, in 20 fathoms, and he has generously presented his largest specimen, the holotype, to the Dominion Museum. There is a larger specimen, but his is the best preserved.
Careful comparison of the New Zealand specimens with C. rudis Hutton and with authentic New South Wales specimens of L. volvox (Reeve) showed C. rudis Hutton and the Australian specimens to be conspecific—indeed, in all probability Hutton's type is an Australian shell—and showed that the New Zealand specimens were a very distinct species not so far described.
In the Manual of the New Zealand Mollusca, 1913, p. 46, pl. 2, fig. 22, Suter records Lorica volvox (Reeve), giving C. rudis Hutton as a synonym, but his accompanying description does not accurately fit either L. volvex (Reeve) or L. haurakiensis, a specimen of which is in his collection. Mr. Murdoch, of Wanganui, points out that the description appears to be derived partly from his New Zealand specimen, partly from C. rudis, and partly from Reeve's description. As we have no record of Lorica volvox (Reeve) being obtained alive in New Zealand, and as the New Zealand species is specifically very distinct, I would suggest that Lorica volvox (Reeve) should be eliminated from our fauna, and Lorica haurakiensis take its place as the New Zealand representative of the genus.
An unfortunate numerical mistake has occurred on plate 2 of Suter's Manual, where Lorica volvox is fig. 24, and Omithochiton undulatus is fig. 22.
The true numbering is Lorica volvox, fig. 22; Onithochiton undulatus, fig. 24. So far as I can tell from the very poor figure, a specimen of L. haurakiensis is there shown, but accurate determination is almost impossible.
Rhyssoplax Thiele (5).
Rhyssoplax oliveri n. sp. (Plate XXXVIII, figs. 9–11.)
Huetataka, Lyall Bay, Cook Strait, N.Z.
Shell small, oval, smooth, with a subglossy surface, the side slopes almost straight. Anterior valve smooth except for six tiny nodules close to the girdle, and slight traces of radial riblets. The animal is dried inside, but the eight slits are easily seen under a pocket-lens. Median valves slightly beaked, the jugal and pleural areas smooth, lateral areas raised, well defined, with very faint traces of radial sculpture. Interior one slit, sinus hidden by the animal, colour bluish, insertion plates probably white. Posterior valve, mucro central, moderately prominent, posterior slope rather steeply concave, bounded by a nearly smooth rib. Interior eight slits.
Colour : Ground-colour cream, mottled with dull green, and small longitudinal flecks of light brown; the whole surface densely covered with microscopic white speckles.
Girdle : Scales very finely closely striate, rounded, the largest along the centre, the outer edge with three or four rows of very fine outstanding spicules, which are easily rubbed off. Colour creamy transversely banded with green and tinged with brown.
Measurements : Length, 10.5 mm.; breadth, 7 mm.
Material : The holotype, obtained by W. R. B. Oliver, 13th January, 1918, and presented to the Dominion Museum.
Remarks.—This species appears to be more closely related to Rhyssoplax translucens (H. & H.), of Australia, than any other New Zealand member of this genus. It differs from R. translucens in being smoother and much smaller, while the girdle-scales are proportionately larger and rounder.
Damoniella Iredale (6).
Damoniella alpha n. sp. (Plate XXXVIII, fig. 12.)
Shell small, narrow, elongately cylindrical, solid. Sculpture about thirty flat spiral ribs, with very narrow grooves between them. The grooves are rendered punctate by a large number of fine vertical growth-striae, which do not cross the spiral ribs. Aperture the entire length of the shell, narrow anteriorly, somewhat inflated posteriorly. Outer lip sharp, very slightly crenulated by the spiral grooves. Vertex pierced by a very narrow axial perforation. Columella short, vertical, slightly concave, very lightly reflexed towards the tiny umbilical chink.
Measurements : Length, 7 mm; breadth, 4 mm.
Material : The holotype, in the Dominion Museum, collected by Dr. J. A. Thomson at Blue Cliffs, Otaio River, South Canterbury, in 1917 (Awamoan).
Remarks.—This specimen was placed by the late Mr. Suter in the genus Roxania Leach (1847), but Iredale points out that this is invalidated by a
prior use of Roxana for a genus of insects, and he proposes Damoniella in place of it, with Bulla cranchi Leach as genotype. So far as I can judge from the description and figures (7), this is a near ally of the new species; there is an Australian species, Atys dactylus Hedley (8), which also appears to resemble it, at least superficially.
1. T. Iredale, 1915. The Chitons of the Kermadecs, Proc. Malac. Soc. Lond., vol. 2, pp. 32–33.
2. T. Iredale, 1915. A Commentary on Suter's Manual of the New Zealand Mollusca, Trans. N.Z. Inst., vol. 47, p. 425.
3. H. Suter, 1913. Man. N.Z. Mollusca, pp. 46–47, and p. 1082.
4. F. W. Hutton, 1872. On the New Zealand Chitomdae, Trans. N.Z. Inst., vol. 4, p. 179.
5. T. Iredale, 1915. A Commentary on Suter's Manual of the New Zealand Mollusca, Trans. N.Z. Inst., vol. 47, p. 426.
6. T. Iredale, 1918. Molluscan Nomenclatural Problems and Solutions, No. 1, Proc. Malac. Soc. Lond., vol. 13, pp. 28–40.
7. H. A. Pilsbry, 1893. Monograph of Tectibranchiata, Man. Conch. (1), vol. 15, p. 27, pl. 28, figs. 28–29.
8. C. Hedley, 1899. The Atoll of Funafuti, Mem. Austral. Mus., No. 3, p. 484.