223 
columella short, spiral : nacre none ; muscular impressions two, 
lateral, distant; a slightly revolving, elevated line on the inner 
surface; operculum none. 
Animal tongue-shaped, chiefly formed by a very long, and very 
• thick foot, which is narrower and massive before, truncated behind, 
canaliculated on each side and widely margining on all sides the 
contorted visceral mass, which is very small, slightly convex above, 
and covered by an interior shell; head depressed; mouth very 
small, concealed under the anterior and superior margin of the 
foot; tentacula two, compressed and appendiculated at base; a 
large branchial pecten ; male organ under the right tentaculum ; 
mantle without emargination. 
Ohs. That able anatomist, Blainville, was the flrst to detect the 
difference between the animal of the much depressed species of 
the genus Sigaretus, Adans., and of those with a more elevated 
spire ; and notwithstanding the similarity of the shells he very 
judiciously separated them and formed the present genus, if we 
may judge by the characters he has stated, for which we rely en- 
tirely on his accuracy. It differs much from Coriocella, Blainv., 
the animal of which has a very small foot and a coriaceous shell. 
C. PERSPECTIOUS, S. 
0. MACULOTUS, S. 
An attempt to exhibit a Synonymy of the Western North American species of 
the genera Unio and Alasmodonta. 
UNIO. 
1. U. NIGER, Rafinesque.* 5. U. fragilis, R. Sw. Deshayes. 
cuneatus, Barnes. gracilis.^ B. Hildr. Lea. Eaton. 
2. U, CARiosus, S. Lam. B. 
viridis, Raf. 
siliquoides^ B. (var.) 
radiatus ? Gm. 
3. U. FASCIATUS, Raf. 
carinatus^ B. 
4. U. LEPTODON, Raf. 
planus^ B. 
purpurescens^ Swainson. 
tenuissimusj Lea. 
6. U. NERVOSUS, R. 
zigzag^ Lea, 
donaciformis^ Lea. 
'I. U. LiEVIGATUS, R. 
" castaneus ? Lea. 
8. U. RECTUS, Lam. Valenc. Eaton. 
latissimus, R. 
prcelongus, B. Hildr. 
9. U, DILATATUS, R. 
nasut7is, Lam. 
gibbosus, B. Hildreth. 
* This writer and some others imitated Lamarck in giving the specific name in 
this genus a feminine termination, which we have changed in this table. 
