63 
This new genus I formerly proposed when describing the above 
KLentioned Unio undulata, under the name of Monodonta ; but as 
this term has been applied to a genus of Univalves, I have substi- 
tuted that of Alasmidonta. 
[A. N. S., vol. ii. p. 149, seqq., Jan., 1821.] 
The terrestrial and fluviatile shells which form the subject of the 
following pages, were chiefly obtained on the late expedition to the 
E-O'cky Mountains, under the command of Major Stephen H. Long. 
They are now deposited in the Philadelphia Museum, and consti- 
tute, in the collection of that institution, a distinct arrangement. 
A few descriptions are added to this essay, of shells discovered 
in East Florida, Alabama, Pennsylvania, and New-York. 
[J. A. N. S., vol. ii. p. 164, et seqq. Jan. 1821.] 
Planorbis armigerus. — Shell dextral, brownish-horn color, 
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 continued to the aper- 
ture ; aperture longitudinally subovate, oblique ] labmm blackish 
on the edge; throat armed with five teeth, placed two upon the 
pillar side, of which one is large, prominent, perpendicular, lamelli- 
form, oblique, and rounded abruptly at each extremity ; near the 
anterior tip, is a small prominent conic acute one ; on the side of 
the labrum is a prominent lamelliform tooth near the base, and 
two slightly elevated, oblique, lamelliform ones above. 
Length, J of an inch nearly. Inhabits Upper Missouri. 
Remarkable by the teeth ; but these are only discoverable by 
the microscopical examination of the mouth, and they are situated 
far within it. 
P. TRIVOLVIS, BICARINATUS and PARTUS inhabit ponds of 
water, in the vicinity of Council BluiF. 
Planorbis parallelus. — Shell dextral, with very minute 
transverse wrinkles, and regular, revolving, equidistant, parallel, 
slightly elevated lines ; spire a little convex ; volutions four ; aper- 
ture longer than wide ; umbilicus exhibiting all the volutions. 
Breadth, less than 3-20 of an inch. Inhabits Upper Missouri. 
