44 
G-enus 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 Grenus Helix. The spire is sometimes 
profoundly sunk, so much so as to be with difficulty distinguished 
from the base. « 
Planorbis trivolyis.— 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, tah. 140. Jig. 46. 
Lister figures this shell pretty accurately, and it is referred to in 
Grmelin^s Edit, of Syst. Nat. p. 3615, as Alhella^ 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. 
