96 TRANS. OF THE ACAD. OF SCIENCE. 



middle) to the ventral margin, whence it arches more ab- 

 ruptly to the posterior extremity (which is above the middle 

 and subangular); valves convex near the umbo, flattened 

 below and concave towards the posterior cardinal border. 

 Surface marked with numerous fine, high and rounded 'con- 

 centric plications. 



Length, .34; height, ,23; thickness, .17. 



This fossil was discovered by Dr. Norwood in the Ste. 

 Genevieve Limestone, back of Prairie du Rocher, Illinois. 



Cypricardia(^) Wheeleri. 



Shell small, subtriangular, widest in front; narrow and 

 pointed at the posterior extremity; distinctly sinuate from 

 the beaks to the posterior ventral margin, making a depressed 

 sharp ridge between it and the posterior cardinal slope: um- 

 boncs large ; beaks curved in and forward. Surface marked 

 with a i'aw concentric stria3. Structure punctate or fibrous. 



This shell resembles the C. occidentalis / but it is much 

 smaller, longer in j)roportion, and marked with concentric 

 stria 1 . 



This fossil was discovered by Mr. Wheeler, in the Upper 

 Coal Measures in Caldwell county, Missouri. 



CvrRICARDIA(?) OCCIDENTALIS. 



Shell large, gibbous, subtriangular. Valves very convex ; 

 flattened towards the ventral margin ; concave towards the 

 posterior cardinal margin, where they form a thin sharp edge 

 at their junction ; slightly sinuate from the beaks to the pos- 

 terior ventral margin : umbones large, full; beaks, near the 

 anterior extremity, large, strongly curved in and forward, 

 contiguous; posterior end narrow and acute; posterior car- 

 dinal margin convex, sloping to the extremity below the 

 middle ; ventral margin convex in front and middle, less con- 

 vex or straight towards the posterior end ; anterior cardinal 

 margin convex, descending rapidly to the wide, slightly con- 

 vex anterior extremity. Surface apparently smooth, with a 

 few obsolete, depressed, concentric folds. Structure punc- 

 tate 



Length, 2.84; height, 2.G0; thickness, 1.98. 



This rare shell was discovered by Mr. Wheeler in Harrison 

 county, Missouri. 



Cypricardia(?) Ciiodteauensis. 



Shell small, transverse, elliptical, plicate, widest in the 

 middle; valves convex from the umbo to the posterior mar- 

 gin, flattened or concave towards the posterior cardinal mar- 



