206 SELEN1TES. 



examined ; whorls 5, rather rapidly enlarging, the last depressed 

 above at the aperture. Diam. 12 mill. 



Puget Sound to San Diego, Cat. 



The striae are sharper than in the larger 'H. Vancouver ensis, 

 so that the revolving lines only show upon the ridges which 

 they cross, and the color is usually somewhat paler. The differ- 

 ence in sculpture between the two species is generally better 

 marked on the base of the shell, which in H. Vancouverensis is 

 much smoother. 



S. CONCAVA, Say. PI. 61, figs 96-98. 



Very widely umbilicated, very pale yellowish or greenish 

 yellow, finely lightly striate, sometimes with microscopic revolv- 

 ing lines ; whorls 5, a little flattened above, well-rounded below, 

 with well-impressed suture, last whorl flattened above at the 

 aperture ; peristome often tinged with chestnut-color. 



Diam. 21 mill. 



Canada, Maine to Michigan, 



south to Georgia and Missouri. 



H. planorboides, Fer., and H. dissidens, Desh., are synonyms. 



The animal is grayish above, with bluish tentacles and eye- 

 peduncles, the pedal disk dirty white, collar and tail tinged with 

 reddish orange ; foot narrow, twice as long as the diameter of 

 the shell. 



As shown by its dentition, this animal is voracious and car- 

 nivorous in its appetite, " almost always," writes W. G. Binney, 

 " preying upon other species with which it may be kept, and so 

 certainly destroying them, that I have been obliged to keep them 

 by themselves. This it effects by inserting its narrow body, 

 which it has the power of elongating and protruding very far 

 from its own shell, into the shells of its victims, and then feeding 

 upon them at its leisure." 



S. VOYANA, Newcomb. PI. 61, figs. 99, 100. 



Widely umbilicated, thin, translucent, with delicate oblique 

 striae, and fine revolving lines, more developed below, very light 

 olivaceous horn-color ; whorls 5, rapidly increasing, the last 

 strongly depressed above at the aperture ; aperture obtusely 



