68 



Of this species, I found two specimens at Bowyer creek, near 

 Council Bluff. It differs from P. heterostropha in magnitude, in 

 having a more elongated spire, and less deeply impressed suture. 



Physa elongata. — Shell heterostrophe, pale yellowish, very 

 fragile, diaphanous, oblong; whirls six or seven; spire tapering, 

 acute at the tip ; suture slightly impressed ; aperture not dilated, 

 attenuated above, about half as long as the shell ; columella much 

 narrowed near the base, so that the view, may be partially extended 

 from the base towards the apex. 



Inhabits shores of Illinois. Length, 7-10 inch. Greatest breadth, 

 8-10 nearly. 



Animal deep black, immaculate, above and beneath ; tentaeula 

 setaceous, a white annulation at base. 



In the fragility of the shell, this species approaches nearest to 

 columella. It is very common in stagnant ponds on the banks of 

 the Mississippi. When the chell includes the animal, it appears 

 of a deep black color, with an obsolete testaceous spot near the base 

 on the anterior side. Its proportions ai-e somewhat similar to those 

 of P. liypaorutn. 



Physa heterostropha (Nicholson's Encyc.) — Is veiy com- 

 mon in ponds of the Missouri as far as Council Bluff. 



Valvata tricarinata (Nicholson's Encyc.) occurs in consid- 

 erable numbers in ponds, in the vicinity of Council Bluff. 



Paludina 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 subovatc, more than half the length of the shell ; labium with 

 much calcareous deposit, and thickened into a callosity at the supe- 

 rior 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 and ponderous species. It bears a striking re- 

 semblance to P. decisa, and has, without doubt, been generally 

 considered as the same ; but it differs from that species in being 

 much more iucrassated and heavy ; and although much decorti- 

 cated and eroded upon the spire, the tip is not truncated. In the 



