167 
Ampularia, and Valvata, and from these, in addition to other 
differential traits it may be distinguished by the disunion above of 
the labise. It strongly resembles Melanopsisy Pirena and Potam- 
ides, but these are distinctly and unequivocally emarginated at 
base. 
The animal respires water ; it has a shorty conic-cylindric, obtuse 
rostrum ; two acute tentacula having the eyes at their exterior base ; 
foot short and obtuse. 
They are inhabitants of fresh water^ chiefly in the tropical re- 
gions ; but many species are very abundant in the rivers^ lakes and 
small streams of the United States. No recent ones have been 
found in Europe^ but several have occurred fossil in comparatively 
recent formations. No fossil species have yet been found in this 
country. Lamarck described sixteen recent and twelve fossil spe- 
cies ; but Defrance enumerates thirty-six species. 
Melania nupera.* — Specific character. From one to four or 
more revolving series of tubercles. 
Ohs. It varies in the number of its series of tubercleS; some 
specimens having but one^ and others^ though these are rare^ as 
many as five or six. Plate 8. Middle figure exhibits the young 
shell. 
Melania depygis.* — Specific character. Body whorl yellow- 
ish^ with two equidistant^ revolving, rufous lines. 
Ohs. It varies a little in color, and a few occurred, of which 
the color is fuscous, the bands being obsolete. PL 8, lower figures. 
Lutraria. — Shell equivalve, inequilateral, transversely oblong 
or subovate, gaping at the extremities, particularly at the posterior 
extremity; cardinal teeth two, of which one is doubled in the 
shape of a Y, the other simple, with a large deltoid cavity situated 
obliquely near the teeth ; lateral teeth none ; ligament internal, in- 
serted in the cardinal cavities, not visible when the shell is closed ; 
muscular impressions two, lateral, remote, simple ; impression of 
the mantle extending to the muscular impressions and having a 
large and profound sinus extending nearly half its length. 
Ohs. Lamarck separated this group from the Linnman Mactrscy 
from which it is essentially distinct by the absence of lateral teeth 
* [Mr. Say makes no reference to the previous descriptions of this spe- 
cies in N. H. Diss. — E d.] 
