162 
very numerous, obsolete greenisb. radii; sometimes witb more or 
less obvious, transverse, yellowish bands towards the base ; beaks 
not elevated above the general surface, witb two or three rows of 
very small tubercles : binge margin nearly rectilinear, compressed 
behind, and anteriorly compressed almost into a wing : ligament, 
particularly in the young specimen, concealed : posterior margin 
rounded : anterior margin a little prominent, obtusely angulated ; 
basal margin much arquated : within undulated almost as obvh 
ously as on the exterior ; pale bluish, varied with^pale flesh color, 
and somewhat iridescent before and behind : cicatrices slightly 
impressed. 
Length about four inches. Breadth five and three-tenths. Con- 
vexity nearly one inch and three quarters. 
A large and fine species. Some time since, Mr. 0. Evans 
obtained an individual, which I hesitated to publish as new, think- 
ing it might possibly be a young remote variety of the A. grandis^ 
nob., but subsequently, having received adult and perfect speci- 
mens from Mr. Evans, I found that it is uniformly longer, more 
rounded, mu«h more compressed, and having a different aspect. 
It is found in ponds, near the Wabash river, but rarely, if ever, in 
the river itself, as it prefers still water and a muddy bottom. In 
form it approaches nearer to orbicular, than any other species that 
we have seen described. 
An American conchologist was of the opinion that all our Ano- 
dontas are referrible to one species ; but we conceive that the 
present species, cannot with more propriety be united with the 
cataracta and marginata, nob., not to mention the more elongated 
species, than the various species of TJnio can be considered as no 
other than TJ. pictaj L. PI. 11. 
Nucula. — Shell transverse, equivalved, inequilateral ; summits 
contiguous ; hinge with a primary, more or less triangular fosset for 
the reception of the ligament, with an anterior and posterior series 
of small, inserted, numerous, pectinate teeth, interrupted at the 
summit by the fosset ; ligament internal, very short, inserted into 
the fosset ; muscular impressions two, simple. 
Ohs. A genus connected with Area, Pectunculus, Cucullsea, 
and Trigonia, but eminently distinguished by the ligament being 
interior; which, as has been remarked by Sowerby, proves their 
relation to the Mactracese. Many species are known. Lamarck 
