578 CRETACEOUS PALEONTOLOGY. 



1876. Cardium (Trachycardium) Huf dense Gabb, Proc. Acad. 



Nat Sci. Phil. (1876), p. 310. 

 Not 1886. Cardium Eufaulensis Whitf., Pal. N. J., vol. I 



(Monog. U. S. G. $., vol. 9), p. 132, pi. 20, figs. 17-19. 



Description. The dimensions of the internal cast of a left 

 valve are : height, 26.5 mm. ; width, 21.5 mm. ; convexity, 9 mm. 

 Shell obliquely ovate in outline. Hinge-line arcuate; anterior 

 and basal margins rounding regularly with slightly decreasing 

 curvature from the anterior cardinal extremity to the postero- 

 basal extremity; postero-basal margin rounded; posterior mar- 

 gin gently convex or nearly straight, always straighter than the 

 anterior margin. Beaks small, acute, incurved, only a little 

 elevated above the hinge-line. Valves strongly convex, with a 

 rounded umbonal prominence passing obliquely backward from 

 the beak to the postero-basal extremity; posterior slope short, 

 abrupt, nearly flat or sometimes slightly concave; anterior slope 

 much longer, convex, becoming a little more abrupt anteriorly. 

 Muscular impressions inconspicuous on the casts, the inner 

 free margins of the valves crenate, surface of the casts some- 

 times smooth, sometimes showing impressions of the radiating 

 ribs half way to the beak from the margin. Outer surface 

 of the valves marked by from 35 to 40 angular, radiating 

 costse, where the shell is exfoliated these ribs appear to be hol- 

 low or tubular and their position is indicated by depressed fur- 

 rows instead of elevations. 



Remarks. The specimens which were referred to this species 

 by Whitfield really belong to two different species, neither one 

 of them being the true C. eufmilensis. The specimens which have 

 been identified as C. eufaulensis in the present report, agree closely 

 with Conrad's original description and illustration, and agree 

 with authentic specimens from the South. They have been recog- 

 nized only in the Wenonah sand, where they are associated with 

 C. longstreeti, but differ from that species in being more elongate 

 and relatively narrower, and more regularly oval in outline with- 

 out the subangular postero-basal extremity. The radiating ribs 

 of the two species are also very different, those of C. eufaulensis 



