548 CRETACEOUS PALEONTOLOGY. 



its generic relations, it is retained in that genus here because it 

 has the general form of authentic species of the genus, and agrees 

 with them rather than with Crassatellites in the absence of crenu- 

 lations upon the inner free margin of the shell. 



Formation and locality. Manasquan marl, Pemberton (191),. 

 near Farmingdale (138). 



Geographic distribution. New Jersey. 



Genus AMBOCARDIA Whitfield. 



Ambocardia cookii Whitfield. 



Plate LX., Figs. 1-2. 



1886. Ambocardia cookii Whitf., Pal. N. J., vol. i (Monog. 

 U. S. G. S., vol. 9), p. 25, pi. 2, figs. 11-14. 



Description. "Shell large and ponderous, with heavy, mas- 

 sive, incurved beaks, which are strongly enrolled and situated 

 near the anterior end of the shell. Valves very gibbous, very 

 inequilateral and transverse, strongly cuneate in a cardinal view 

 when united, being extremely ventricose opposite the beaks and 

 gradually but rapidly decreasing in depth toward the posterior 

 end; obliquely ovate in outline, with a short, obtusely pointed 

 anterior end, straight but short cardinal line; prolonged but 

 obtusely rounded posterior end; basal line strongly curved, rap- 

 idly declining from the anterior end, and distinctly sinuate near 

 the middle of the shell by a broad, shallow, but well-defined 

 oblique sulcus, which passes from the beak to the basal margin 

 just in front of the strongly rounded and prominent umbonal 

 ridge. External ligament strongly marked, and extending the 

 length of the posterior cardinal line and deeply imbedded in a 

 narrow escutcheon. Lunule large and deep, strongly defined, 

 with sharply angular margins. Substance of the shell thick and 

 dense, and the surface marked with close comparatively strong 

 concentric lines or ridges, and apparently with a thick epidermis. 

 Anterior muscular scar large and deep, situated close to the mar- 

 gin in the pointed anterior end. Other muscular imprints not 



