652 TRANS. OF THE ACAD. OF SCIENCE. 
and rounded in front. Ventral valve very convex, strongly 
arched longitudinally; umbo large; beak large, strongly in- 
curved; perforation subovate ; mesial sinus wanting or rare- 
ly obsolete. Dorsal valve less convex, most prominent near 
the beak, ovate, flattened in front; umbo large; beak short, 
incurved beneath and cutting into the periphery of the per- 
foration of the opposite beak; mesial fold wanting. Surface 
marked with numerous concentric lines of growth, which be- 
come very distinct and sublamellose near the margin. It is 
also ornamented with very fine concentric and radiating 
strie. 
Length, 1.32; breadth, 1.02; thickness, .63. 
This fossil was discovered by Dr. Norwood, in the Upper 
Coal Measures of Cass county. 
SprriceRaA Hawnit, n. sp. 
concentric and still finer longitudinal strie ; when partly ex- 
foliated, it exhibits small longitudinal costs ; the whole punc- 
tate. 
Length, .84; width, .76; thickness, .55. 
Length, .90; width, .73; thickness, .82. ae 
This fossil is most like Sp. subtilita of Prof. Hall, but it v3 
more gibbous, more elliptical and has the fine striations dif- 
ferent from that species. 
Coal Measures of the State of Missouri. 
PENTAMERUS SALINENSIS, N. sp. 
Shell small, ovate, plicate, with a long pointed beak on se 
ventral valve. Ventral valve gibbous, highest near the beak; 
gradually arched towards the anterior margin, but much wot 
abruptly towards the lateral and cardinal borders; flattene 
in front and marked with nine or ten depressed plications 
