SCIENCE-GOSSIP. 



244 



ARMATURE OF HELICOID LANDSHELLS. 



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



(Continued from page 207.) 



JJLECTOPYLIS cydaspis (5gs. 34a-rf), from 

 Tenasserim, Burma, was first described by 

 Mr. Benson, under the name of Helix catinus, in the 

 "Annals and Magazine of Natural History" (3), 

 iii. (1859), p. 1S5, but that name being preoccupied 

 in Helix he changed it to Helix cyclaspis (loc. cit., 

 p. 273). Having received additional material, 

 which enabled him to examine the armature, he 

 subsequently published an amended description 

 (loc. cit. (3), V. (i860), p. 245). The shell was first 

 figured in Hanley and Theobald's " Conchologia 

 Indica," t. 13, f. 10 (1870). The anatomy has been 

 figured by Mr. F. Stoliczka in the " Journal of the 

 Asiatic Society of Bengal," xl. (1871), p. 222, t. 15, 

 ff. 4-6, and by Mr. Pilsbry in " Manual of 

 Conchology, ix. (1895), t- 42, ff. 34-3G, while the 

 palatal armature has been illustrated by Lieut. - 



Fig. 34. — Plcctopylis cyclaspis. 



Colonel Godwin-Austen in the " Proceedings of the 

 Zoological Society," 1874, t. 74, f. 10. The shell is 

 sinistral, depressed-conical, widely umbilicated, 

 irregularly ribbed above, smoother below, hornish 

 brown, with the suture margined ; it is composed 

 of six and a-half or seven slowly increasing whorls, 

 the last not descending in front, and having an acute, 

 compressed keel . The peristome is thickened and re- 

 flexed and its margins are united by a raised straight 

 ridge; the parietal callus bears a short, strong 

 horizontal entering fold, entirely visible from the 

 aperture (see fig. 34^). The parietal armature con- 

 sists of a strong and very complicated ramified plate, 

 which ascends obliquely from the side of the aperture 

 near to the suture, where it bifurcates, one arm — 

 the upper one — ascending a little, then proceeding 



February, 1897.— No. 33, Vol. 3. 



horizontally, and finally becoming attenuated ; the 

 lower and stronger one descends obliquely at an 

 angle of 45^ for about half its length, then 

 deflects almost vertically and gives off posteriorly 

 at its base a short strong support. The lower 

 extremity of the main plate gives off anteriorl} 

 also a strong short support. Below the plate is a 

 free, short, horizontal fold. The specimen shown 

 with the outer wall removed in fig. 346 is not quite 

 mature, and it possesses the former plate, which is 

 evidently in course of absorption, as the second 

 descending arm has almost disappeared, and the 

 lower free fold is also very slight. The palatal 

 armature consists of five folds : the first, thin, near 

 and almost parallel with the suture ; the second, 

 broad and flexuous, descending obliquely posteriorly, 

 half above and half below the peripherial keel ; the 

 third, also broad and somewhat crescent-shaped ; 

 the fourth, very strong, broad and vertical, and 

 intercalating with the main stem and lower branch 

 of the parietal plate ; the fifth, thin, horizontal and 

 parallel with the lower suture. Fig. 34c shows 

 the parietal and palatal armature from the anterior 

 side, while ^^d shows the inside of the outer wall 

 with its palatal folds. At the base of the vertical 

 palatal fold on the right side — i.e. posteriorly — 

 occurs a small denticle, shown erroneously in 

 fig. 34(f, on the left side. Fig. 34a shows a mature 

 specimen, natural size ; the other figures are all 

 magnified. The two specimens are from Moulmain, 

 Burma, and are in the collection of Mr. Ponsonby. 

 The mature specimen measures — major diameter, 

 17 millimetres; minor diameter, 14.5 millimetres; 

 axis, 7 millimetres. 



Plectopylis hareuorjcm (figs. 35^-^), from Pegu, was 

 described by Mr. W. T. Blanford in the "Journal 

 of the Asiatic Society of Bengal," xxxiv. (1865), 

 part 2, p. 73, and figured by Dr. Pfeiffer in 

 "Novitates Conchologicae," iii. (1869), t. loS, 

 ff. 16-18, and in Hanley and Theobald's " Con- 

 chologia Indica," t. 13, f. 6 (1870). The armature 

 was figured by Lieut. -Colonel Godwin Austen in 

 the " Proceedings of the Zoological Society," 1874, 

 t. 74, f. 5. According to Mr. G. Nevill (" Handlist 

 of MoUuscain the Indian Museum. Calcutta " (1878) 

 p. 72), the species has also been found in the Arakan 

 Hills. The shell is sinistral, disk-shaped, with the 

 apex a little raised above the flattened spire, with 

 a wide but shallow umbilicus, white with light 

 chestnut strigations, finely ribbed, with micro- 

 scopic spiral sculpture. It is composed of six 

 closely-coiled whorls, which increase siow'y, the 



