300 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS, 



With a New Section of Plectopylis. 



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

 (Continued from page 276.) 



TDEFORE resuming the consideration of other 

 ■*-^ Burmese and Indian species of Plectopylis, I 

 will deal with a small section of the genus 

 characterized by a thin and transparent shell 

 and a peristome with straight, acute edges. 

 Two species only have hitherto been known, 

 P. clathratida, from Ceylon, and P. retifera, from 

 India ; but a third undescribed form, also from 

 India, has been communicated to me by Colonel 

 Beddome : two species from Ceylon, described and 

 figured by Dr. F. Jousseaume in the " Memoires de 

 la Societe Zoologique de France," vii. (1894), 

 pp. 277 and 278, t. 4, ff. I and 8, have been referred 

 by him to Plectopylis, and, if correctly thus referred, 

 they will doubtless be found to belong to this 

 section, for which I propose the name A ustenia, in 



Fig. 42. — Plectopylis clathratula. 



honour of Lieut. -Colonel Godwin- Austen, who has 

 contributed so largely to our knowledge of the 

 genus. 



Plectopylis clathratula (figs. 42fl-^), from Ceylon, 

 was described by Dr. Pfeiffer in the " Zeitschrift 

 fiir Malakozoologie," vii., (1850), p. 67. It 

 was figured in Reeve's " Conchologia Iconica," 

 t- 65, f. 336 (1852), in Martini und Chemnitz's 

 " Conchylien Cabinet," 2nd ed., iii., t. 127, 

 ff. 17-20 (1853), and in Hanley and Theobald's 

 "Conchologia Indica," t. 132, ff. 1-4 (1875). Mr. 

 Benson described what he thought was a new 

 species, under the name of Helix puteola, in the 

 "Annals and Magazine of Natural History" (2), 

 xii. (1853), p. 92, but he subsequently pointed out 

 its identity with Dr. Pfeiffer's species (loc. cit. (3), 

 V. (i860), p. 247). It was also figured under Mr. 

 Benson's nameby Reeve, op. cit., 1. 190, f. 1334(1854). 

 Mr. G. Nevill (Hand List, p. 70) records P. clathratula, 

 as in the Indian Museum, Calcutta, from Balapiat, 

 Sikkim ; but I doubt the correctness of the identifica- 

 tion of the specimens referred to and think they will 

 probably prove to belong to the new species to be de- 

 scribed in the next article as Plectopylis clathratuloides. 



As the armature of Plectopylis clathratula has never 

 been figured, I am pleased to have an opportunity 

 of illustrating it. The shell is somewhat lenticular, 

 widely umbilicated, pale corneous, transparent, 

 showing the palatal armature distinctly through 

 the shell-wall. It is finely and regularly striated 

 by raised ribs, which are more prominent above 

 than below, it is acutely keeled at the periphery, 

 and has two raised spiral ridges revolving near the 

 peripherial keel and ascending as far as the second 

 whorl. It is composed of 5J slowly increasing 

 whorls, a little convex above, inflated around the 

 wide and deep umbilicus. The base of the shell is 

 shining. The peristome is simple, straight and 

 acute, the left margin being a little reflected over 

 the umbilicus. The parietal armature consists of a 

 single, slightly oblique, vertical plate, which is 

 slightly twisted and a little notched in the middle, 

 and gives off posteriorly above an obliquely 

 ascending support (see fig 42^^, which shows the 

 shell with part of the outer wall removed). The 

 palatal armature appears to be somewhat variable, 

 and consists of various denticles, arranged princi- 

 pally in two horizontal series, midway between the 

 periphery and the umbilicus. In the specimen 

 figured, which is in Mr. Ponsonby's collection, the 

 first series consists of : posteriorly, a short, strong, 

 flattened vertical tooth, and anteriorly, two short, 

 slight, horizontal denticles, separated by a short 

 space, the second series consists of: posteriorly, 

 a short, flattened, vertical tooth, a little smaller 

 than the one above it, and, anteriorly, a short, 

 oblique, curved denticle. Below these two series 

 is a longer, but thin, horizontal fold, coincident with 

 the umbilical angulation, while above the vertical 

 tooth of the first series is a minute, horizontal 

 denticle, coincident with the peripherial keel. The 

 specimen measures 5 millimetres in diameter. 

 (Fig. 42a shows both armatures from the posterior 

 side, the anterior palatal denticles being hidden by 

 the posterior teeth ; fig. 426 gives the anterior view 

 of both armatures, but the posterior tooth of the 

 first series is here hidden by the parietal plate ; 

 fig. 42c shows the palatal folds as they appear from 

 below through the shell-wall ; all the figures are 

 enlarged.) Two specimens in my collection — 

 measuring, major diameter 6 millimetres, minor 

 diameter 5-5, axis 3 millimetres — have the anterior 

 portion of the first series, consisting of four 

 horizontal denticles, the first two close together, 

 the third a little smaller and further distant, and 



