SCIENCE-GOSSIP. 



178 



ARMATURE OF HELICOID LANDSHELLS. 



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



(Continued from page 156.) 



'PLECTOPYLIS ponsonbyi (figs. 22a-e), from 

 ■^ Hlindet, Burma, was described by Lieut. - 

 Colonel Godwin -Austen in the " Proceedings of the 

 Zoological Society "for 1888, p, 243. My draw- 

 ing has been prepared from the specimen figured 

 by Mr. Pilsbry in " Manual of Conchology," ix. 

 (1894), t. 40, figs. g-i2. The shell is sinistral, 

 disk-shaped, flattened above, with the apex a little 

 raised, composed of six and a-half whorls, closely 

 and regularly coiled, rounded and gradually in- 

 creasing ; it is regularly and finely ribbed, and has 

 the last whorl deflexed in front ; the parietal callus 

 has a raised flexuous ridge, which is separate above 

 and below from the peristome. From the aperture 

 may be discerned a short, free, slightly curved, 

 parietal fold, which follows the deflexion of the 

 last whorl (see fig. ■22a). The parietal armature 



Fig. 22.— Plectopylis ponsonbyi. 



further consists of two strong vertical plates, the 

 posterior one of which is the longer of the two ; 

 it gives off posteriorly at the upper extremity a 

 very short horizontal ridge, and at the lower 

 extremity another short, but stronger, ridge, which 

 descends obliquely ; the anterior plate is shorter 

 but much stronger and thicker than the posterior 

 one, and it gives off two strong ridges, one from 

 the upper and one from the lower extremity, 

 gradually decreasing in height. Below these two 

 vertical plates there is a very thin horizontal fold 

 terminating posteriorly a little beyond the posterior 

 vertical plate, and anteriorly becoming attenuated 

 till it is scarcely visible at the parietal ridge, to 

 which, however, it is united. In the figure referred 

 to, I regret to find this horizontal fold is wrongly 

 shown as terminating a little beyond the anterior 

 vertical plate. The palatal armature consists 



December, 1896.— No. 31, Vol. 3. 



of : first, a thin horizontal plate, parallel with and 

 near to the suture, a little broader in the middle ; 

 secondly, a somewhat stouter plate, slanting a little 

 downwards posteriorly, also a little broader in the 

 middle, and decreasing abruptly anteriorly, but 

 very slowly posteriorly, where it is slightly 

 indented ; thirdly, a similar plate, slanting a little 

 more posteriorly, with a slight indentation ; 

 fourthly, a stout bilobed vertical plate giving off 

 anteriorly at the upper extremity a very slight 

 ridge and posteriorly from the base of each lobe a 

 short ridge ; fifthly, a horizontal fold parallel with 

 and near to the lower suture, raised in the middle, 

 with the apical portion reflexed and angular; it 

 has a very small tooth on the posterior side. 

 Another very small tooth is situate a little below 

 the first horizontal plate about its middle, shown 

 erroneously in fig. 22(f in a line with it. Fig. 22b 

 shows the whole armature from the side of the 

 aperture, fig. 22c the same from behind, and fig. 

 22d the inside of the outer wall with the palatal 

 folds (all magnified) ; while fig. 22f shows the shell 

 restored, from above, natural size. The type 

 specimen measures 18 millimetres in diameter, and 

 is in Mr. Ponsonby's collection. 



Plectopylis fultoni (figs 23a and b) was described 

 by Lieut. -Colonel Godwin-Austen in " Annals and 

 Magazine of Natural History " (6), x. (1892), p. 

 300, where the habitat of Khasi Hills, India, is 

 doubtfully given, but the exact locality is unknown. 

 The species was subsequently figured in Mr. 

 Fulton's advertisements in "Nature" and "The 

 Nautilus," and these figures were incorporated by 

 Mr. Pilsbry in his " Manual of Conchology" (vol. 

 ix., t. 40, ff. 13-15). As, however, the armature 

 has not hitherto been figured, I am pleased to 

 have an opportunity of doing so. The shell 

 is sinistral, subglobosely disk-shaped, widely 

 umbilicated, of a pale ochreous colour, regularly 

 ribbed and decussated by a fine spiral sculpture ; it 

 is composed of seven or seven and a-half whorls, 

 very slowly increasing in width, the last of which 

 descends in front ; the body whorl bears four rows 

 of coarse hairs revolving horizontally over its 

 whole length, the first on the keel, the second a 

 little below the first, the third midway between the 

 second and fourth, the latter being near the 

 umbilical angulation. The peristome is reflexed 

 and thickened ; the parietal callus is only slightly 

 thickened, its margin, however, is distinctly 

 separated from the peristome above and below ; 

 the aperture is devoid of armature. The shell 

 measures 18 to 20 millimetres in diamexer. The 



