15 



terior part of the shell ; crossed by fine elevated concentric 

 lines of growth, more or less closely arranged. Near the 

 basal margin are some stronger subimbricating ridges par- 

 allel to the lines of growth. 



Length, '33 to *50 of an inch. 



Locality. — Spergen Hill ; Bloomington. 



Conocardium Prattenanum. — Shell sub-fusiform ; hinge 

 line straight, beaks depressed, distinctly anchylosed ; from 

 the beaks along the anterior umbonial slope, angle obtuse and 

 scarcely defined ; anterior side obtuse, convex in the mid- 

 dle, and gradually sloping upwards from the angles ; pos- 

 terior part of the shell with a broad depression on each 

 side, and again expanding at the extremity with an oblique 

 angular fold, from the hinge line downwards to the hiatus ; 

 hiatus broad and expanded behind, narrowed abruptly at 

 the junction of the oblique folds, and thence gradually to 

 the middle of the shell. Surface marked by strong plica- 

 tions, which are much stronger on the anterior part of the 

 shell, and more slender behind. The fold along the anterior 

 umbonial slope bifurcates, sending off on each side a plica- 

 tion, which again bifurcates. Plications crossed by sharply 

 elevated lines, which are more conspicuous on the posterior 

 part giving it a cancellated appearance. 



Length, *20 of an inch. 



Locality. — Alton, 111. 



Conocardium Meekanum. — Shell sub-angularly ovate or 

 abruptly clavate ; hinge line nearly straight, declining at the 

 posterior extremity and sometimes from the beaks ; oblique- 

 ly truncated anteriorly ; anterior end convex in the middle, 

 and margined by a narrow sulcus which reaches from beak 

 to base just within the obtuse angle of the umbonial slope ; 

 posterior end sloping on the base uniformly from the centre 

 of the shell to the extremity, contracted behind the body 

 of the shell ; vertically depressed and slightly expanded 

 laterally at the extremity. Surface marked by small, ele- 



