654 TRANS. OF THE ACAD. OF SCIENCE. 
lar; anterior margin rounded. Dorsal valve smaller, most 
convex along the middle, subflattened towards the lateral 
margins, highest near the beak ; beak large, pointed, ineury- 
ed beneath and in contact with the opposite beak. Surface 
marked with numerous small, depressed, radiating cost, and 
by fine concentric strie and a few distinct lines of growth. 
Length, 1.22; breadth, .95; thicknes 
not so wide in front. It also resembles some varieties of 
hastata of Sowerby, but its markings will always distinguish 
it from that species. 
Very rare in the Chemung rocks of Cooper and Benton 
counties, 
Retzia (?) Poreana, nh. sp. 
Shell elongate, subovate, widest near the middle, rounded 
in front, subeuneate towards the beaks; gibbous near the 
beaks, but much flattened towards the front and lateral mar- 
gins, where the valves form a sharp, thin edge. Ventral valve 
Length, .1; breadth, .71; thickness, .42. 
This fossil may be distinguished from ZR. Osagensis by a 
want of coste. It resembles R. fusiformis of M. Verneuil, 
with which it has been confounded, but it is very distinct It 
is thickest near the beaks, and is much more compressed in 
form than the specimens of the European shell before me. 
ACEPHALA. 
Epmonpia MARIONENSIS, N. sp. 
Shell large, gibbous, sub-quadrangular. Valves very “ieee 
vex ; flattened or concave towards the posterior cardinal bor- 
