284 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS, 



With a New Form of Plectopylis. 



By G. K. Gude, F.Z.S. 



[Continued jtom page 264.) 



pLECTOPYLIS DIPTYCHIA (figs. 71a-/), from 

 the province of Kouei-Tchou, China, was 

 described by Dr. von Mollendorff in the " Jahrbuch 

 der Deutschen Malakazoologischen Gesellschaft," 

 xii (1885), p. 390, and the shell was figured in the 

 same work, t. 10, f. 17. No figure of the armature, 

 as far as I have been able to ascertain, has hitherto 

 been published ; my readers will, therefore, be glad 

 to be able to form an idea of these structures from 

 the accompanying figures. The shell is dextral, 

 discoid, light corneous, thin, sub-pellucid, finely 

 striated, decussated with microscopic spiral lines 

 above, shining below, widely and deeply umbi- 

 licated. The cuticle is produced into distant 

 plaits, which are very prominent at the periphery. 

 The spire is a little raised, and the suture is 

 impressed. There are six narrow whorls, which 

 increase slowly and regularly, the last is angulated 

 above the periphery, rounded below, not deflected 

 in front. The aperture is roundly lunate, oblique ; 

 the peristome white, a little thickened and reflexed, 

 the margins scarcely united by the parietal callus, 

 which is devoid of any ridge at the aperture. The 

 parietal armature consists of two strong vertical 

 plates, slightly converging above ; the anterior one 

 curved, with the convex side towards the aperture, 

 giving off anteriorly at the upper extremity a short 

 horizontal ridge, and being a little deflected 





J 



d e 1 



Fig. yi.— Plectopylis diptychia. 



posteriorly below. The posterior one is crescent- 

 shaped, strongly deflected posteriorly below (see 

 fig. 71/, which shows the parietal wall of the shell 

 with its two plates). The palatal armature is 

 composed of six short, more or less horizontal 

 folds; the first very minute, near the suture: the 

 second, third, fourth and fifth obliquely deflected 

 posteriorly ; the sixth horizontal (see fig. yie, 

 which shows the inside of the outer shell-wall with 

 its folds). The specimen figured measures : major 



diameter, C millimetres ; minor diameter, 5 milli- 

 metres ; altitude, 3 millimetres. It was sent to me 

 by Dr. von Mollendorff, and is now in my collec- 

 tion. All the figures are enlarged. 



Plectopylis viurata (figs. 72a and b), from Tchen- 

 K'eou, China, was described and figured by Mr. 

 Heude, in Part 2 of his " Notes sur les Mollusques 

 terrestres de la Vallee du Fleuve Bleu " (1885), 

 p. 112, t. 30, f. 1. The shell is dextral, discoid, 



Fig. 72. — Plectopylis viurata. 



light corneous, finely striated and decussated with 

 microscopic spiral lines above, smooth and shining 

 below. On the upper side, the cuticle is produced 

 into distant persisting plaits, which form a coarse 

 fringe around the periphery. The spire is a little 

 elevated, and the suture linear. There are five 

 and a-half to six whorls, which increase regu- 

 larly, and are flattened above and rounded below ; 

 the last does not descend in front, and is 

 keeled at the periphery. The aperture is 

 rounded, oblique ; the peristome white, a little 

 thickened and reflexed, its margins being united 

 by a slight ridge on the parietal callus ; the 

 umbilicus is wide and deep. The parietal armature 

 is similar to that of Piectofylis steuocliila (see my 

 note in this series of papers, Science-Gossip, N.S., 

 Vol. iii. p. 204, figs. 29/j and d), and is as variable as 

 in that species. The number of denticles in front 

 of the vertical plate in Plectopylis murata varies 

 from one to three, or such denticles may be absent 

 altogether, while the upper and lower short hori- 

 zontal folds in front of the vertical plate, may be 

 reduced to denticles. The palatal armature is 

 also similar to that of Plectopylis stenochila (he. 

 cit. figs. 29c and d), to which species the present 

 one is closely allied, but the shell is more 

 depressed, and the whorls are flattened above 

 with the base shining and translucent, while 

 in Plectopylis stenochila the whorls are rounded 

 above with the base striated and opaque. In the 

 species under consideration there are only five and 

 a-half to six whorls, and the umbilicus is more 

 widened at the last whorl, which is keeled at the 



