SCIENCE-GOSSIP. 



263 



ARMATURE OF HELICOID LANDSHELLS, 



With a New Species of Plectopylis. 



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



[Continued from page 232.) 



pLECTOPYLIS OGLEI (figs. 68a-//), from 

 Sadiya, Assam, was described and figured 

 by Lieut. -Colonel Godwin-Austen in the "Journal 

 of the Asiatic Society of Bengal," xlviii. (1879), 

 p. 3, t. I, f. 2. The shell is dextral, disk-shaped, 

 widely umbilicated, corneous, marked transversely 



Fig. 68.~Plfctopylis oglei. 



with dark brown, finely and closely striated, the 

 upper side coarsely decussated with raised spiral 

 lines. The spire is scarcely raised, the apex a 

 little elevated, and the suture impressed. There 

 are eight rounded whorls, which increase slowly 

 and regularly, the last being angular above and 

 below, and obsoletely keeled at the periphery, 

 descending slowly in front. The aperture is 

 oblique, roundly ovate, slightly depressed above ; 

 the peristome is white, thickened and reflexed, its 

 margins are connected by a scarcely raised curved 

 ridge on the parietal callus, a slight notch being 

 observable above and below at the junctions. The 

 parietal armature consists of a single strong 

 vertical plate, which gives off posteriorly two short 

 ridges, one at the upper and one at the lower 

 extremity (see fig. 68^, which gives an enlarged 

 view of a specimen with the outer wall removed). 

 The palatal armature consists of six horizontal folds : 

 the first, near the suture, very short and thin ; the 

 second, third, fourth, fifth, and sixth, bilobed 

 or bisected about the middle, where a slight 

 vertical ridge connects their posterior portions ; 

 the posterior portion of the second fold is sinuous, 



February, i8g8.— No. 45, Vol. IV. 



somewhat S-shaped ; the third, fourth, and fifth 

 are slightly deflected posteriorly ; the sixth is very 

 unequally bisected, the posterior portion being 

 less than a third the length of the anterior por- 

 tion, which is raised at first and then suddenly 

 deflected (see fig. 680', which shows the inside 

 of the outer wall of the shell enlarged). The 

 illustrations have been made from the type 

 specimens in the collection of Lieut. -Colonel 

 Godwin-Austen, to whom I am under obligation 

 for the loan of them. The specimen shown in 

 figs. 68a-c (natural size) measures ; major diameter, 

 27 millimetres ; minor diameter, 25 millimetres ; 

 altitude, 8 millimetres; figs. 68e-g (enlarged), are 

 taken from a specimen not quite full-grown ; 

 e shows the parietal and palatal armatures from 

 the anterior side ; /, their posterior aspect ; and g, 

 as just mentioned, the inside of the outer wall with 

 its folds. This specimen exhibits the remains of a 

 previous parietal plate, one quarter of a whorl 

 behind the permanent one. Fig. <58/j, shows the 

 inside of a portion of the outer shell-wall of the 

 specimen shown in fig. 68d, the armature of which 

 is incomplete, a portion having been broken away. 

 Two immature specimens in different stages of 

 growth exhibit armatures identical in all respects 

 with those illustrated, except that the palatal folds 

 are less bilobed. The species under consideration 

 is allied to Plectopylis serica, but it is larger, and 

 presents considerable difterences in the palatal 

 armature. 



Fig. 69. — Plectopylis munipiirensis. 



Plectopylis inunipurciisis (figs. 69^-^), from the 

 Ihang Valley, Munipur, was described and figured 

 by Lieut. -Col. Godwin-Austen in the " Proceedings 

 of the Zoological Society," 1874, p. 610, t. 73, f. 6. 



