AND ALLIED FORMS. 



2T 



This genus I take pleasure in dedicating to my esteemed asso- 

 ciate Prof. Theodore Gill, in recognition of his great ability as 

 a malaeologist, and of the assistance he has rendered me in the 

 determination of the conchological characters of the animals now 

 under consideration. 



The .shell in this genus is thin or only moderately thickened, 

 simply striate, short, subconic, scarcely umbilicated, and with the 

 body whorl subglobose, the spire rather small, and the suture not 

 impressed. The aperture is ovate, regularly rounded in front, 

 angular behind, with its peritreme thin and acute, appressed 

 behind internally to the whorl, and with its entire margin in the 

 same plane, which is very oblique, .sloping downwards and Ijack- 

 wards. The operculum is thin, and its margin concave within 

 near the upper end. 



The soft parts of Gillla altilia resemble those of the preceding 

 two genera in the robust form of the body and snout, but differ 

 considerably in other respects. The foot (Fig. 19, h) is oblong, 

 broadly rounded behind, and strongly auri- 

 cled in front. The tentacles (see in Fig. 

 19, a) are long, slender, and pointed. The 

 eyes are placed on the outer sides of tuber- 

 cles at the outer bases of the tentacles. 

 The verge (see in Fig. 19, a) is very small, 

 simple, compressed, and lunate or sickle- 

 shaped ; being thus strikingly different from 

 that of the genera previously described in 

 this paper. The colors of the animal re- 

 call those of the Melanians more than those 

 of Amnicola proper, being very dark, and 

 minutely mottled, as if peppered in. 



The lingual dentition (Fig. 20) is of a 

 character in some respects intermediate 



Fig. 19. 



2§P 



Fig. 20. 



