OF THE UNITED STATES* 173 



denominates it " Buccinum exiguum Ritfum quinq 

 orbium." This shell does not perfectly correspond 

 in character with Cyclostoma ; it is most probably a 

 Pupa, and if so the specific name must be changed, 

 as the present name is pre- occupied in that genus. 



Genus Valvata. 



V. triccttinata (Nicholson's Encyc.) occurs in 

 considerable numbers in ponds, in the vicinity of 

 Council Bluff. 



Genus Paludina. 



1. P. *ponderosa. Shell somewhat ventricose., 

 much thickened, olivaceous or blackish ; spire not 

 much elongated, much shorter than the aperture, 

 eroded at tip, but not truncated ; whirls five, slightly 

 wrinkled across ; suture profoundly impressed}; aper- 

 ture sub-ovate, more than half the length of the shell j 

 labium with much calcareous deposit, and thickened 

 into a callosity at the superior angle ; within tinged 

 with blue. 



Inhabits Ohio River. 



Greatest length one inch and 11-20. 



Transverse diameter one inch and 1-10. 



This shell is common at the falls of the Ohio, and 

 is a very remarkably thick aud ponderous species* 

 It bears a striking resemblance to P. decisa, and has 

 without doubt, been generally considered as the same ; 

 but it differs from that species in being much more 



