64- 



This shell has evidently the habit of a Helix, and may probably 

 belong more properly to that genus, but having found it only in a 

 dried up pond, in company with a vast number of aquatic shells, I 

 refer it for the present to this genus. 



Planorbis exacuous*. — Dextral, depressed, with an acute 

 edge. 



Inhabits Lake Champlain. Cabinet of the Academy. 



Shell depressed ; whorls four, striated across, wider than long, 

 not elevated above the suture, but a little flattened, sides obliquely 

 descending to an acute lateral edge, below the middle ; spire not 

 impressed ; suture not profoundly indented ; beneath, body whorl 

 flattened, on the inner edge rounded ; umbilicus regular, exhibit- 

 ing all the volutions to the apex ; aperture transversely sub-trian- 

 gular ; labrum angulated in the middle, arquated near its inferior 

 tip, the superior termination just including the acute edge of the 

 penultimate whorl. 



Greatest breadth, rather less than 1 of an inch. 



This species was found in Lake Champlain by Mr. Augustus 

 Jessup, who deposited it in the collection of the Academy. Only 

 two specimens occurred. It may be readily distinguished fi-om P. 

 parvus, by its more convex form above, the spire not being im- 

 pressed, and by its very acute lateral edge. It appears to be pretty 

 closely allied to Planorhis nitidus of Europe, but it is larger, 

 the umbilicus much more dilated, and the aperture does not em- 

 brace the penultimate whorl so profoundly. 



Planorbis campanulatus. — Sinistral; whorls longer than 

 wide ; aperture sub-campanulate. 



Inhabits Cayuga Lake. Cabinet of the Academy. 



Shell sinistral, not depressed ; whorls four, slightly striate across, 

 longer than wide ; spire hardly concave, often plane ; body whirl 

 abruptly dilated near the aperture, and not longer behind the dila- 

 tation than the penultimate whirl ; suture indented, well defined 

 to the tip, the summits of the volutions being rounded ; aperture 

 dilated ; throat narrow abruptly ; umbilicus profound, the view 

 extending by a minute foramen to the apex. 



[* It would certainly appear that Mr. Say intended this word to read 

 exacutus, as Dr. Gould suggests, — yet the same orthography is retained 

 in Long's Exp. — Ed.] 



