26 
OBSERVATIONS. 
This large species is remarkable for its resem- 
blance to two very different species, U. alatus , of 
Say, and U. ater , of Lea; it has an outline not unlike 
the former, but is less winged and much more con- 
vex; it is less inflated and more elongated than the 
latter, and is more angulated and truncated on the 
posterior margin. The cardinal teeth are directed 
obliquely forwards in U. ater ; in this species they 
are, on the contrary, directed obliquely backwards. 
It is not an uncommon species in the Black Warrior 
river, in JMorth Alabama, where I procured them 
in six or eight feet water, in the centre of the stream; 
the purity of the water enabled me to detect them 
with facility, although a very small portion of the 
shell projected above the surface of the mud in w T hich 
they were always imbedded. I obtained them by 
means of a long pointed stick, with the extremity 
inserted between the gaping valves, which the ani- 
mal immediately closed with such force, that I could 
readily draw them from their tenacious beds. 
UNIO T 2E N I A T U S . 
Plate IV.— Fig. 2. 
DESCRIPTION. 
Shell regularly convex and elliptical, moderately 
thick, epidermis finely wrinkled, olivaceous, with 
regular green interrupted rays; beaks slightly promi- 
nent; umbonial slope rounded; ligament slope with a 
slightly impressed line; base arcuated; cardinal and 
lateral teeth prominent; within bluish white. 
