THE NATURAL HISTORY SURVEY. 293 
Animal: With a rather wide foot (6x34 mill.) rounded be- 
fore and behind; tentacles rather long and filiform, as long as, 
or longer than, the foot; head rounded and not so much auric- 
ulated as in ¢#zvolvis; color blackish, flecked with white on the 
foot and tentacles; respiratory tube large, blackish, flecked 
with white; eyes placed as usual. 
Jaw: As in the genus. 
Radula formula: #1+3+4+8+44+44+ 4421 (30—1—30); cen- 
tral tooth as usual; lateral teeth of the usual shape, but reflec- 
tion with a large, squarish central cusp, a large, rounded inner 
14 
Fic. 97. 
Radula of PLANORBIS BICARINATUS Say. (Original.) c, central tooth; 
1, first lateral; 9, intermediate tooth; 12, third marginal; 25, outer marginal. 
cusp and a smaller outer cusp; intermediate teeth with three 
nearly equal, rather sharp cusps; marginal teeth as usual ( Fig. 
97). The writer counted 136 rows in one membrane. 
Genitalia: Not examined. 
Distribution: United States and Canada, from New Eng- 
land to Manitoba, and south to New Mexico. 
Geological distribution: Pleistocene. 
Hlabitat: In rivers and ponds, in water from two to ten or 
fifteen feet in depth, on a muddy bottom: 
Remarks: Bicarinatus is at once distinguished by Shee pecu- 
liar, cone-shaped depression on both the upper and lower sur- 
face, and by the characteristic v-shaped part of the aperture 
which rises above the body whorl. The species is quite abun- 
dant but is difficult to obtain alive on account of its preferring 
deep water. The animal is rather slow in movement, the head 
is carried much farther in advance of the foot than in “#zvolvvs. 
It is an interesting sight to see one of this species crawling up 
