124 Mr. Barnes on the Genera Unio and Alasmodonta. 
ligament deeply inserted between the valves; hinge-margin 
nearly straight, compressed alated, heel-shaped, and making 
an obtuse angle with the anterior margin; basal margin 
rounded ; epidermis light green, tinged with reddish brown; 
surface of the anterior part studded with irregular transverse- 
ly compressed tubercles. Cardinal teeth crenated or sul- 
cated; cavity of the beaks very deep, compressed angular 
and directed backwards under the cardinal tooth; Naker 
brownish red with a tinge of blue, or light chocolate color- 
ed, slightly iridescent on the anterior part; the other dull 
and not highly polished; posterior muscular impression 
deep and rough. 
Variety (a.) has the epidermis of an uncommonly light 
green without the browr tinge. 
Hab. Lake Erie. Major Delafield’s collection. 
Diam. ‘8 Length, 1°65 Breadth, 1°9 
Variety (b.) is a slender and rather thin shell; epidermis 
very pale green; Naker pearly white, polished and irides- 
cent. 
Diam. ‘9 Length, 1°6 Breadth, 1-9 
Locality and authority as before. 
Remark.—If a straight line is drawn from the beak to the 
base, through the cardinal tooth, it will divide the tubercu- 
lated from the smooth part of the shell, in all except the va- 
-riety (6.) in which the tubercles extend a little farther 
back. 
_ 7%. Unio Nodosus. Fig. 7. ag inside. 
b. outside. 
Shell, sub-quadrangular, sub-longitudinal, emarginate be- 
fore, knotted, ridged, corrugated; lateral tooth terminating 
abruptly. 
Hab. Ouisconsin. Mr. Schoolcraft. 
Collections of Lyceum and Dr. Mitchill. 
ollection. 
m. 1°8 Length, 2°5 Breadth, 3-0 
Shell, thick and ponderous, short and very obtusely 
rounded behind ; beaks distant, elevated, eroded, chalky or 
greenish white, with the ligament passing between them. 
Anterior lunule, compressed, wedge-shaped, separated by @ 
deep groove, ending inthe emargination in front. Hinge-mer- 
