154 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS. 



Bv G. K. GuDE, F.Z.S. 



{Continued from page 128.) 



II. Plectopylis. 

 T N the genus Plectopylis, now to be considered, we 

 find the armature more complicated than in 

 Corilla. In the latter, we have seen the parietal 

 plates to be invariably more or less horizontal, 

 and the palatal plates — normally four in number — 

 to be either horizontal or oblique, and always 

 simple. The species of Plectopylis, however, are 

 characterized by the possession of vertical as well 

 as horizontal barriers, which in some cases are 

 double, frequently bifurcate or ramified, and the 

 plates or folds are often very numerous. The genus 

 contains a far greater number of species than 

 Corilla (more than fifty being known), and it has a 

 much wider range, being found over the whole of 

 the Indian Peninsula, including the Himalayan 

 Range, Burma, Cambodia, Tongkin, extending north 

 to Central China, with three species in Ceylon, 

 and a reputed single outlier in the Andaman Islands. 

 The Philippine Islands are credited with four species, 

 but the absence of a vertical barrier on the parietal 

 wall renders their position in the genus somewhat 

 doubtful; as the anatomy of the soft parts, how- 

 ever, has not, to my knowledge been studied , it 

 may be advisable for the present to retain these 

 four species in Plectopylis. Many of the species are 

 sinistral ; dextrorsity, however, is the rule. 



Plectopylis andersoni (figs, i.'ja-c), which was des- 

 cribed by Mr. W. T. Blanford, in the "Proceed- 

 ings of the Zoological Society" for 1869, p. 448, 



Fig. 17. — Plectopylis andersoni. 



was found near Bhamo and Ava, in Upper 

 Burma, and on the Yun-nan frontier. It is a 

 solid, disc-shaped shell, measuring 24 to 26 

 millimetres in diameter, of a light brown colour, 

 with alternating streaks of a lighter shade on the 

 upper surface. It is composed of eight whorls, 

 distinctly ribbed above and below, and very 

 regularly decussated above by raised spiral lines 

 reaching as far as the apex of the shell, the base is 

 also spirally sculptured, but the sculpture is less 

 distinct ; the mouth of the shell is unarmed, but the 

 parieial callus forms a raised curved ridge which is 



distinctly free at both ends from the peristome. 

 The armature, which is comparatively simple, 

 occurs a little beyond the middle of the last whorl, 

 and consists of a simple strong vertical plate on the 

 parietal wall (see fig. 17a), giving off at its upper 

 extremity a very small horizontal tooth on the 

 posterior side and a short horizontal lamella, 

 I, 5 millimetres long, on the anterior side, while 

 at its lower extremity there is a slight callus on 

 the posterior side. The vertical parietal plate 

 is shown sideways in fig. ijb, where also the 

 palatal teeth are seen as they appear from the 

 posterior end. Fig. lyc, gives the inside view of 

 the outer wall, exhibiting the palatal armature. 

 The palatal armature consists of four principal 

 horizontal lamellae terminating posteriorly in a 

 triangular conical tooth ; above these are : first 

 a minute tooth, and secondly, higher up, a small 

 fold near the suture, while at the base of the 

 palatal wall are also : first a minute tooth, and 

 secondly, nearer the suture, a small fold. The 

 specimen figured is from Mr. Ponsonby's collection. 

 Plectopylis bracliydiscus (figs. i8a-c) was described 

 and figured by Lieut. -Colonel Godwin- Austen, in the 

 "Journal of the Asiatic Society of Bengal," xlviii. 



Fig. iS.— Plectopylis brachydiscus. 



(1879), p. 2, t. I, f. I, from specimens found on the 

 highrange of Mule-it, eastofMoulmein,Tenasserim. 

 As in that work, however, the palatal arma- 

 ture is not figured, I am glad to be able to 

 supplement the figures there given. The speci- 

 men now figured, from Mr. Ponsonby's collection, 

 is old and weatherworn, and it does not possess 

 the marginal fringe of hairs shown in Lieut. -Colonel 

 Godwin-Austen's figure. The shell is described 

 as being of a dull umber brown ; it is disk- 

 shaped and regularly coiled, consisting of seven 

 whorls, finely ribbed and spirally striated above ; 

 it measures 19 millimetres in diameter. The 

 peristome is strongly reflected and the parietal 

 callus has a strong, raised, flexuous ridge, 

 separated from the peristome, and has, in 

 addition, about the middle, a free lamella, 3 

 millimetres long (see fig. i8a). The parietal 

 armature consists further of a broad, vertical 



.rtclVEMHF:!, J896. — No. 30, Vol. 3. 



