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. Grreatest breadth, 
3-10 nearly. 
Animal deep black, immaculate, above and beneath ; tentacula 
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 are somewhat similar to those 
of P. hypnorum. 
Physa heterostropha (Nicholson’s Encyc.) — Is very 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. 
Paludtna 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 subovate, 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 Biver. 
(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 incrassated and heavy ; and although much decorti- 
cated and eroded upon the spire, the tip is not truncated. In the 
