AND ALLIED FORMS. 25 



tion, its soft parts (Fig. Ifi) are described below in their con- 

 tracted state. The foot, which is folded in the specimen figured, 

 is short, somewhat contracted at the middle, broadly rounded be- 

 hind, and auricled(?) and bimarginate in front. 

 The operculigerous lobe is simple, little de- 

 veloped, and smaller than the operculum, 

 which latter is thin, horny, subovate, and 

 subspiral, with about three turns. The ros 

 trum (Fig. 10, a) is quite large, broad and 

 flattened, somewhat rectangular, bilobate in 

 front, and wrinkled transversely — resembling 

 in its general characters that of the Mela- 

 niidse much more than that of Amnicola. 

 The tentacles in their contracted state about 

 equal the rostrum in length ; they are somewhat tapering, but 

 flattened, and apparently bluntly pointed at their tips. The 

 eyes are barely perceptible, and are situated on slight protuber- 

 ances at the outer bases of the tentacles. The branchial cavity 

 (laid open in the figure) is shallow. The mantle edge is simple. 

 The gill (Fig. 16, dl) is very broad in front, but becomes narrower 

 behind ; it consists of about twenty low subtriangular plates, much 

 less projecting than in Amnicola, and sharply acuminate at the 

 tip of the projection. The verge (Fig. 16, h) is large, flattened, 

 broader than long, and placed obliquely on the right side of the 

 neck, some little distance behind the right tentacle. It has on the 

 left side and posteriorly a great wing-like expansion, the surface 

 of which is striated transversely. This verge, though not bilid 

 as in the preceding genus, is homologous in form, the wing corres- 

 ponding to the left fork of the organ in Somatogyrus isogo7ius. 



The oviduct of the female lies on the mantle, parallel to the 

 rectum, filling the space between this latter sack and the line n 

 junctui-e of the mantle with the body ; its orifice is situated a 

 little within the margin of the mantle, immediately below the 

 anus. In the rectum (Fig. 16, c) the ftecal matter is broken into 

 fusiform pellets. 



The lingual dentition is as follows : — The rhachidian tooth is 

 broad, but longer in proportion than in Amnicola and Somato- 

 gijrus, and trilobate below, the middle lobe being triangular, but 

 not acute ; the basal denticles, on the surface beneath the lateral 

 margins, are three in number on each side, rather long and slender, 



