164 UNIVALVE SHELLS 



of an inch. I observed one specimen, which was 

 upwards of an inch long. 



Genus Planorbis. 



1. P. *annigprus. Skell dextral, brownish-horn 

 colour, wrinkles obsolete ; spire perfectly regular, 

 slightly concave; suture well impressed; umbilicus 

 profound, exhibiting the volutions: whorls four, 

 longer than wide, obtusely carinated above, carina 

 obsolete near the aperture, a carina beneath conti- 

 nued to the aperture ; aperture longitudinally sub- 

 obovate, oblique; labrum blackish on the edge ; 

 throat armed with five teeth, placed two upon the 

 pillar side, of which one is large, prominent, per- 

 pendicular,lamelliform, oblique, and rounded abrupt- 

 ly at each extremity ; near the anterior tip, is a 

 small prominent conic acute one ; on the side of the 

 labrum, is a prominent lameliiform tooth near the 

 base, and two slightly elevated, oblique, lameliiform 

 ones above. 



Leugth, 1-4 of an inch nearly. 



Inhabits Upper Missouri. 



ilemarkable by the teeth; but these are only dis- 

 coverable by the microscopical examination of tht 

 mouth, and they are situated far within it. 



P. trivolvis b earn ius and parvus inhabit ponds 

 of water, in the vicinity of Council Bluff. 



2. P. * } arallellus. Shell dextral, witb very mi- 

 nute transverse wrinkles, and regular, revolving, 



