MOLLUSCA. 579 



being broader, less abruptly elevated from the interspaces, and 

 lacking the small nodes upon their summits. The specimens ob- 

 served vary somewhat in outline, some individuals being rela- 

 tively lower and broader than the one whose dimensions are 

 given. 



Formation and locality.— Wenonah sand, near Crawfords Cor- 

 ner (126^). 



Geographic distribution. — New Jersey, North Carolina, Ala- 

 bama, Mississippi, Arkansas. 



Cardium longstreeti n. sp. 



Plate LXIIL, Pigs. 21-22. 



Description. — The dimensions of the internal cast of a left 

 -valve are: height, 33 mm.; width, 31 mm.; convexity, 10 mm. 

 Shell obliquely subovate in outline. Hinge-line arcuate; antero- 

 cardinal margin nearly straight,, sloping downward from the 

 beak to the anterior hinge extremity, curving below without 

 break into the anterior margin; anterior and basal margins 

 rounding with a regular, slightly decreasing curvature from the 

 anterior hinge-extremity tO' the postero^basal extremity ; postero- 

 basal extremity subangular, situated considerably above the base 

 of the shell ; posterior margin obliquely truncate, rounding above 

 tO' the posterior hinge-extremiity. Beaks small, acute, incurved, 

 moderately elevated above the hinge-line, pointing slightly back- 

 ward at their tips. Valves with an umbonal prominence passing 

 obliquely from the beak to the postero-basal extremity, in the 

 ■casts it is subangular, but in the shell itself more rounded; the 

 most prominent portion of the shell lies in front of this umbonal 

 ridge; posterior slope narrow, somewhat flattened or concave; 

 anterior slope gently convex across the middle of the shell, be- 

 coming more abrupt towards the anterior margin. The inner 

 free marg'ins of the shell strongly crenate, and the radiating ribs 

 present upon the internal casts half way or more toi the beaks. 

 Muscular impressions inconspicuous upon the casts. Surface 

 ■of the shell marked by about 38 rather high, angular ribs with 

 small, more or less distant nodes along their summits; these 



