FAUNA CANADENSIS. 505 



26. Limncea, sp. 



A small undetermmed species allied to Limnce.a columella, Say. 



Hab. — Rare in from one to two fathoms in Toronto Bay. 

 27. Physa lieterostroplia, Say. 



Shell sinistral, with a ventricose and capacious body-whorl. Spire 

 short, of three whorls, acute. Suture distinct. Aperture about 

 three-fourths as long as the shell, somewhat oval, acute posteriorly. 

 The outer lip thin ; the inner lip thickened in front. 



Colour dark brown, semi-transparent. Size variable ; length of 

 large specimens from one half to seven-tenths of an inch. 



Hah. — Common in shallow water at the " Island." 

 28. Physa, sp. 



A small fragile, horn-coloured form, much resembling the preceding 

 in most respects, and, perhaps, its young. 



Hah. — Rare in from one to three fathoms. 



29. Cyelas similis, Say. 



Shell transversely oval, with strongly convex, nearly equilateral 

 valves. Anterior and posterior margins nearly equally rounded, the 

 anterior slightly the most so. Base nearly straight. Umbones 

 nearly central, directed slightly forward, obtuse. Surface with 

 numerous, regular, concentric striae. Cardinal teeth, two in number, 

 minute, oblique. Lateral teeth elongated, oblique, bifid on one side. 

 Colour paler or darker brown, sometimes with a greenish tinge ; 

 internally bluish white. 



Transverse diameter from one half to seven-tenths of an inch ; 

 vertical diameter from three to five-tenths of an inch. 



Hah. — Common in from one to three fathoms. 



30. Pisidium abditum, Haldemand. 



Shell minute, ovate, concentrically striated, inequilateral. Umbones 

 directed anteriorly. Anterior margin obtusely rounded ; posterior 

 margin somewhat pointed ; base slightly rounded. Shell ventricose ; 

 beaks in contact. Colour yellowish-brown or flesh-coloured. Trans- 

 verse diameter one-tenth of an inch ; vertical diameter the same, or 

 slightly less. 



Hah. — Common in from one to five fathoms. 



31. Jliiio erassidens, Lamarck, 

 Common, both in the living and the dead state, in from one to 

 three fathoms in Toronto Bay. 



