13 



valve extremely gibbous, without sinus, arcuate, marked by 

 five or six elevated distant concentric undulations which are 

 ornamented upon their dorsal margins by a single row of 

 elongate pustules or nodes ; and on their middle and basal 

 margins by numerous smaller granulations ; beak attenuate 

 and extremely arcuate ; ventral valve semi-oval, flattened 

 near the base, having the greatest concavity near the beak, 

 which is obtuse ; surface of the ventral valve marked by 

 eight or nine closely arranged, concentric bands, which are 

 marked by granulations as in the dorsal valve ; hinge line 

 scarcely so wide as the greatest width of the shell ; ex- 

 tremities rounded. 



Locality. — Alton, 111. ; Bloomington, Ind. 



L Productus indianensis.— Shell sub-ovate,gibbous,inflated ; 

 dorsal valve without sinus, gradually contracting towards 

 the beak which is large and strongly arcuate, obtuse at the 

 extremity and very gibbous below ; surface pustulose or 

 aculeate, marked by extremely fine, concentric striae, and a 

 few irregular undulations ; pustules or bases of spines ir- 

 regularly distributed over the surface of the shell, with a 

 linear series down each side below the hinge extremity; 

 hinge line apparently less than the width of the shell. 

 Locality. — Spergen Hill. 



PLEURORHYNCUS, Phillips ; CONOCARDIUM, Bronn. 



Conocardium CATASTOMUM. — Shell very small, elongate, 

 sub-cylindrical or subclavate, gibbous in the middle ; beaks 

 minute, rising slightly above the hinge line, and anchylosed, 

 anterior end obliquely truncated and obtusely angular on 

 the umbonial slope ; the anterior tubular wing minute ; pos- 

 terior end much extended, and constricted near the middle, 

 swelling at the extremity and gaping below. Surface mark- 

 ed with small simple radiating folds which sometimes become 

 obsolete on the anterior end and umbones. Minute undu- 



