63 



This new gcniis I formerly proposed when describing the above 

 mentioned Unio nndulafa, 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 

 Rocky 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 ; labrum 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 abmptly 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, \ 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 PARVUS inhabit ponds of 

 water, in the vicinity of Council Bluff. 



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. 



