52 
it is founds but is not so obtuse in front, and is much less rounded 
at the hinge margin it is also much thinner, and the beaks ap- 
proach each other more closely. 
Unio nastjttjs. — Shell thin, oblong, compressed, rostrated, horn 
color or fuscous, with fine crowded wrinkles obscurely radiate with 
green; within bluish-white; beak cavity hardly any ; teeth crenate. 
Length, one inch and one-eighth : breadth, two and three-fifths. 
Very common in the Delaware and Schuylkill. Plate 4, fig. 1. 
3Iusculus fuscus, augustior, exaltera parte Guneatim protensus. 
Lister, Conch, tab. lbl,Jig. 6. 
Unio alattjs. — Shell moderately thick, sub-triangular, gener- 
ally gaping at the posterior part of the base, fuscous, wrinkled ; 
beaks not prominent, placed very far back and decorticated ; base 
almost rectilinear ; hinge margin remarkably oblique, rising near 
the termination of the cartilage into an alated proj ection, and form- 
ing almost a right angle with the inferior slope, which is nearly 
equal in length ; within red-purple, often with numerous tubercles, 
which, upon the gaping limb, are confluent ; cicatrices very rough ; 
teeth crenate, the external laminated one obsolete, only one in each 
valve being very perceptible. Length, including the projection, 
three inches and four-fifths ; breadth, five inches and a half. Plate 
4, fig. 2. 
Encyc. Meth. vol. 63, tab. 248, Jig. 1, a, b f 
Mr. Lesueur found this species in Lake Erie, very thin and 
fragile. 
The specimen from which this description is taken, and also the 
next species, were purchased by Mr. Joseph Watson, at the sale of 
the late Professor Barton’s collection, and by him presented to the 
Academy of Natural Sciences of Philadelphia. There is also a 
specimen in the Museum of Mr. Peale. 
Unio cylinduicus. — ^Shell very thick, sub-cylindrical, emargin- 
ate before, pale horn-color varied with greenish ; hinge margin 
undulated obliquely across the wrinkles, rough on each side, rec- 
tilinear and parallel to the base ; beaks broad and prominent, with 
a deeply impressed posterior lunule ; within perlaceous, teeth thick 
and crenate ; cavity of the beaks very deep. Length, one inch 
and three-tenths ; breadth, three inches and one-fifth. Plate 4, 
flg. 3. 
