1881.] LAKES TANGANYIKA AND NYASSA, ETC. 289 



horn-colour, banded with white beneath the suture. Whorls 12; 

 first two or three convex, the rest nearly flat, slowly increasing, 

 finely striated by the very flexuous lines of growth. Suture simple, 

 hardly oblique. Aperture small, occupying nearly 5 of the total 

 length. Labrum and columella as above described. Length 1 1^ 

 millims., diam. 3 ; aperture 3 long, 2 broad. 



Hab. Lake Tanganyika (Thomson). 



Besides the lines of growth, some species show traces of spiral 

 Btriation. 



27. Ampullaria gradata, sp. nov. (Plate XXXIIL figs. 22, 

 22 a.) 



Shell globose, narrowly umbilicated, rather thin, moderately 

 glossy, sculptured with oblique distinct lines of growth and minute 

 spiral striae invisible to the naked eye, yellowish olive, with several 

 bands and lines of a greenish tint. "Whorls 6, depressed and flat- 

 tened above, convex at the sides. Spire gradated, worn at the pur- 

 plish-brown apex, equalling about one fourth of the total length. 

 Aperture pyriform, whitish within at the upper part, and light brown 

 elsewhere, with the bands and lines of a vivid dark brown colour : 

 those on the upper part stop short at a little distance from the margin 

 of the lip, leaving a narrow space of a sulphur colour ; those lower 

 down extend almost to the edge, where they are particularly bright. 

 Lip thin, with scarcely any internal thickening. Columella below 

 the umbilicus well curved, expanded, yellowish, connected with the 

 upper extremity of the labrum by a very thin callosity. 



The following are the measurements of the three largest spe- 

 cimens : — 



Hab. Lake Nyassa, and between it and the east coast (Thomson). 



The affinities of this species, if it be distinct, are rather with 

 those forms found in Nilotic regions than with A. speciosa of Phi- 

 lippi from Zanzibar. Tlie four species A. wernei, Pliilippi, A. kor- 

 dofann, Parreyss, A. lucida, Parreyss, and A. ovata, Olivier, are very 

 closely related ; and it is a matter of impossibility to define the 

 limiting characters of any of them. The present species also may 

 only be another form of the same shell. Like A. wernei and A. kor- 

 dofana, the whorls are flattened at the top, so that the spire has a 

 gradated appearance ; but from these it may be distinguished by its 

 broader and shorter aperture and the considerably greater arcuation 

 or incurvation of the columella ; or the form may be described as 

 more pyriform, being narrower above and broader below than in 

 either of those two species. The banding within is of a deep tor- 

 toiscshell browu. and only extends to the margin of the tip, along 

 the base, and about halfway up the side. 



