44 



Grenus Planorbis. — Shell discoidal ; spire depressed, or con- 

 cave ; aperture oblique, rounded, broader than long, visible from 

 above, and emarginated by the convexity of the penultimate whorl ; 

 lips not reflected ; whorls lateral. 



Animal aquatic, with two filiform tentacula, having the eyes 

 placed at the inner base ; operculum none. 



Obs. The species for which this genus was constructed were 

 included by Linnaeus in his Genus Helix, The spire is sometimes 

 profoundly sunk, so much so as to be with difficulty distinguished 

 from the base. 



Planorbis trivolvis. — Shell sinistral, pale yellow, brownish 

 or chestnut color, subcarinate above and beneath, particularly in 

 the young shell ; whorls three or four, striate across with fine, 

 raised^ equidistant, acute lines, forming grooves between them. 

 Spire concave ; aperture large, embracing a considerable portion of 

 the body whorl, within bluish white ; lip a little thickened in- 

 ternally, and of a red or brownish color, vaulted above ; umbilicus 

 large, exhibiting the volutions. Length one-fourth of an inch ■ 

 breadth one-half of an inch. 



Animal aquatic, dark ferruginous, with very numerous, confluent, 

 pale yellowish points; tentacula long, setaceous, with confluent 

 points ; foramen on the left side. 



That ingenious naturalist, Mr. C. A. Lesueur, found this species 

 of a much larger size in French Creek, near Lake Erie ; breadth 

 three-fourths of an inch nearly ; color almost black, purplish red 

 within the mouth. 



Cochlea, trium orhium. Lister. Conch, tab. 140. fig. 46. 



Lister figures this shell pretty accurately, and it is referred to in 

 Gmelin's Edit, of Syst. Nat. p. 3615, as Albella, but it is certainly 

 not that species. Plate 2, fig. 2. 



Planorbis bicarinatus. — Shell sinistral, pale yellow or brown- 

 ish, subcarinate above, and beneath translucent. Spire retusum- 

 bilicate, forming a cavity as deep as that of the base. Aperture 

 large, embracing a considerable portion of the body whorl, and 

 much vaulted above. Within red brown, with two white lines cor- 

 responding with the carina. Whorls three, wrinkled, and with 

 minute revolving lines. Length one-fourth of an inch ; breadth 

 nearly half an inch. 



