74 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS. 



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

 (Continued from p. 17J 



pLECTOPYLIS reperaissa (figs. ySa-/), from 

 Tavoy, Burma, was described by Dr. Gould in 

 the " Proceedings of the Boston Society of Natural 

 History," vi. (1S56), p. 11 ; but as the diagnosis is 

 somewhat vague and as the species was not illus- 

 trated, subsequent authors have considered it to be 

 synonymous with P. achatina, from which species, 

 however, it differs in outward appearance as well 

 as in its armature. The shell is sinistrorse, disk- 

 shaped, pale corneous, finely striated, the upper 



raised flexuous ridge, slightly notched above and 

 below at the junctions. The parieta armature is 

 very complicated, being of the same type as in 

 Plectopylis karenomm, described and illustrated in 

 this series of papers (Science-Gossip, N.S. iii. 

 Feb. 1897, p. 245, f. 35). These two species, 

 together with Plectopylis achatina, P. aiigitiiia and P. 

 linterae, to be considered afterwards, form a distinct 

 group, connected with the group of P. ponsonhyi 

 by a transition form, represented by a single 



Fig. ■/i.—Plectopylis repercussa. 



side being strongly decussated by spiral lines, 

 almost obgolete at the side, but reappearing in the 

 umbilical region. The spire is a little raised, the 

 suture linear. There are seven regularly coiled 

 whorls, which increase slowly and gradually, and 

 are flattened above and tumid below. The last 

 whorl is tricarinated, one keel being at the periphery, 

 one above, and another belov/ (in young shells these 

 keels are provided with a fringe of coanse hairs) ; this 

 whorl widens suddenly at the aperture, where it is 

 deeply deflected. The aperture is almost horizontal, 

 elliptic cordate ; the peristome white, thickened, 

 and strongly reflected ; the margins united by a 



August, 1898.— No. 51, Vol. V. 



specimen as yet undescribed, received by me 

 from Mr. Robert Cairns, of Hurst, Ashton- 

 under-Lyne. A long, stout, horizontal median 

 fold, given off at the apertural ridge, proceeds 

 parallel with the last whorl for a quarter 

 of the length of that whorl, when it gives off a 

 shortly descending, slightly reflected arm, provided 

 anteriorly at the lower extremity with a short, 

 abruptly descending horizontal ridge; the fold 

 then rises obliquely for a short distance, and finally 

 bifurcates ; the loiver arm of the bifutcalion the shorter, 

 and descending almost vertically ; it js provided 

 posteriorly with a short horizontal ridge at its 



D 



