NATURAL SCIENCES OP PHILADELPHIA. 183 



terior side rounded ; base more broadly rounded ; posterior side obliquely sub- 

 truncate above and passing with an abrupt curve into the base below ; hinge 

 margin rather short, and sloping slightly from the beaks, which are moderately 

 elevated, gibbous and nearly central ; posterior umbonal slopes angular ; sur- 

 face of cast retaining only traces of small radiating costae or lines on the pro- 

 minent posterior umbonal slopes, and flattened postero-dorsal region ; hinge 

 and interior unknown. Length 0-44 inch ; height 0-37 inch ; thickness 0-32 

 inch. 



Named in honor of Dr. George G. Shumard, of the Texas Geological Survey. 



Locality and position. Jurassic, beds south-west base of Black Hills. 



Tancredia? jsquilateralis, M. & H. Shell very nearly equilateral, mode- 

 rately convex ; anterior end rather narrowly rounded ; base forming a broad, 

 regular, semielliptic curve; posterior end slightly truncate on the upper oblique 

 slope, narrowly rounded below, apparently not gaping ; beaks depressed, loca- 

 ted a little in advance of the middle; surface of cast retaining traces of con- 

 centric striae ; hinge and interior unknown. Length 1 inch ; height 0-64 inch ; 

 breadth about 0-16 inch. 



Locality and position. South-west base Black Hills Jurassic. 



Tancredia Warrenana, M. & H. Shell small, trigonal ovate, moderately 

 convex, anterior half a little narrower and more compressed than the other, 

 narrowly rounded at the extremity ; base forming a broad gentle curve ; pos- 

 terior side subtruncate, angular, or abruptly rounded below; dorsum sloping 

 from the beaks, the anterior slope being slightly concave in outline, and the 

 other nearly straight, or a little convex; beaks elevated, but not extending 

 much above the cardinal edge ; posterior umbonal slopes prominent, or sub- 

 angular ; surface and hinge unknown. 



Named in honor of Lieut. G. K. Warren, U. S. Top. Engineers. 



Length 0-50 inch; height 0-33 inch ; breadth about 014 inch. 



Locality and position. Same as last. 



Astarte fragilis, M. & H. Shell small, rather broad oval, thin, moderately 

 compressed; anterior end rounded; base nearly straight along the middle, 

 rounding up regularly in front, and more abruptly behind : posterior extremity 

 obscurely subtruncate; dorsum straight and slightly declining behind the 

 beaks, which are small, obtuse, rather depressed, and located a little in advance 

 of the middle; posterior umbonal slopes prominent; surface ornamented by 

 distinct, irregular concentric wrinkles and fine parallel striae ; hinge and interior 

 unknown ; pallial margin crenulate within. Length 0-45 inch ; height 0-32 

 inch ; breadth or convexity 0-18 inch. 



Locality and position. South-west base of the Black Hills Jurassic. 



Astarte inornata, M. & H. Shell subelliptical, compressed; extremities 

 rounded, the posterior margin forming a broader curve than the other; base 

 semielliptical in outline; dorsum declining from the beaks, the anterior slope 

 being a little concave, and the other nearly straight or slightly convex ; beaks 

 moderately elevated, compressed, angular in front, located just in advance of 

 the middle ; lunule rather deep, lance-oval, bounded on each side by a more 

 or less distinct angle ; surface marked by concentric stria?, with a tendency to 

 develop small, very obscure concentric wrinkles. Length 1-15 inches ; height 

 0-79 inch : breadth or convexity 0-44 inch. 



Locality and position. Same as last. 



Trigonia Conradi, M. & H. Shell rather small, subtrigonal, moderately 

 convex; anterior side truncate; base rounded ; posterior side sloping obliquely 

 frorn the beaks above, and apparently vertically truncate at the extremity; beaks 

 elevated, narrow, incurved, and located in advance of the middle ; posterior 

 umbonal slopes distinctly angular ; surface ornamented by rather small, 

 obscure concentric costa?, which on the posterior side of the valves, descend 



I860.] 



