Lower Potsdam Rocks at Troy, N. Y. 139 
ength 0°18 of an inch; breadth 0:12. Occurs in _even- 
bedded limestone of the Lower Potsdam at Troy. Collected 
by the writer. 
The characters of this species agree very closely with those 
of Leperditia Solvensis Jones,* from the Menevian group of 
Wales; but our species is larger, a little different in shape, and 
provided with a distinct eye-tubercle. They appear, however, 
to be very nearly related. 
In the limestones at Troy there occur certain small lamelli- 
branchiate-like shells whose affinities I shall leave for the pre- 
margin uniformly rounded. In the interior of the left sain 
: ; ences and Magazine of Natural History, 2d series, vol. xvii, Feb., 1856, 
