ii4 



SCIENCE-GOSSIP. 



ARMATURE OF HELICOID LANDSHELLS 



AND NEW FORMS OF PLECTOPYLIS. 



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



{Continued from page 76.) 



T)LECTOPYLIS achatina (figs. 80a-/, Sia-d and 

 ■*• &2a-c), from Moulmain, Burma, was des- 

 cribed by Dr. Pfeiffer, in the " Zeitschrift fur 

 Malakozoologie," 1845, p. 86, and Mr. Benson gave 

 notes on the animal, in the " Annals and Magazine 



Fig. 80.— Plectopylis achatina. 



of Natural History" (3), iv. (1859), p. 95. The 

 shell was figured in Hanley and Theobald's " Con- 

 chologia Indica," t. 13, f. 1 and 4 (the latter figure 

 purporting to represent P. repercussa.) Mr. Stoliczka 

 described and figured the anatomy of the animal 

 in the " Journal of the Asiatic Society of Bengal," 

 xl. (1871), p. 221, t. 15, f. 1-3, and Lieut. -Colonel 

 Godwin-Austen, the parietal armature of the shell 

 in the "Proceedings of the Zoological Society," 

 1874, t. 74, f. 6. The shell is sinistrorse, disk- 

 shaped, very widely umbilicated, of various shades 

 of chestnut, usually paler and sometimes flammu- 

 lated below, irregularly and finely striated. The apex 

 is usually, but not invariably, raised slightly above 

 the plane of the whorls. There are six or six and 

 a-half whorls, which increase gradually, and are 

 more or less flattened above and tumid below ; the 

 first three and a-half are smooth or nearly so, 

 while the next two are somewhat coarsely striated 

 and strongly decussated by spiral lines, less dis- 

 tinct on the upper side of the last whorl, obsolete 

 at its side, but reappearing in the umbilical region. 

 The last whorl is bluntly keeled above and sub- 

 angulated at the periphery ; this whorl suddenly 

 widens at the aperture where it is deeply 

 deflected. The aperture is almost horizontal, 



elliptic cordate, while the peristome is thick- 

 ened and strongly reflected, livid or purplish- 

 brown in colour, never white; the margins are 

 united by a raised sinuous ridge, slightly 

 notched at the junctions above and below. The 

 parietal armature is of the same type as that 

 of P. repercussa (ante p. 74, f. 782), but the lower arm 

 of the bifurcation is the longer of the two (see fig. 80c, 

 which shows part of the parietal wall with the 

 posterior portion of its armature), and the lower 

 free horizontal fold close to the lower suture does 

 not reach as far as the apertural ridge, and does not extend 

 beyond the lower arm of the bifurcation and its' posterior 

 support. Fig. 80a gives the anterior and fig. 806 

 the posterior aspect of both armatures. The 

 palatal armature is also similar to that of P. 

 repercussa, but the first horizontal fold is shorter 

 in the present species correspondingly with the 

 reduction in the upper arm of the bifurcation of 

 the parietal armature, while the vertical plate is 

 less strong and its edge less thickened. Plectopylis 

 repercussa is, generally speaking, a more solid and 

 larger shell, always lighter in colour than P. 

 achatina, while its white peristome will at once 

 distinguish it from the latter species. The lower 

 horizontal parietal fold in P. repercussa is always 

 distinctly united to the apertural ridge, whereas in 

 P. achatina this fold is not visible from the aperture. 

 That these characters are constant, I have reason 

 to believe from having opened sixteen or eighteen 

 specimens without finding any variation in these 

 respects. The specimen shown in figs. Soa and b 

 measures : major diameter, 22 millimetres ; minor 



Fig. 81. — Plectopylis achatina juv. 



diameter, 17 millimetres ; altitude, 7 millimetres ; 

 while the one shown in figs. 8od-f measures 

 27 : 21 : 8 millimetres ; both are from Moul- 

 main, and are in my collection. Another 

 specimen in my collection shows no trace of 



