562 CRETACEOUS PALEONTOLOGY. ' 



:ated at about the anterior third of the shell's length. Antero- 

 cardinal margin sloping steeply forward from the beaks ; anterior 

 margin rounded from the lower extremity of the lunule into the 

 regularly convex ventral margin ; postero-basal extremity round- 

 ing somewhat abruptly into the gently convex, obliquely sub- 

 truncate posterior margin ; postero-cardinal margin sloping back- 

 ward from the beak to the posterior extremity of the hinge-line. 

 Free margin of the shell crenate internally. Valves prominently 

 rounded along an oblique line from the beak to the postero-basal 

 extremity, but without a distinct umbonal ridge. Surface of the 

 shell marked by more or less irregular concentric lines of growth, 

 and by more or less indistinct radiating costae, which are finer 

 in front becoming regularly larger posteriorly, the larger ones 

 being a little over one millimeter in width. 



Remarks. This species is the largest member of the genus rec- 

 ognized in the fauna of the Manasquan marl, and occurs most 

 commonly in the form of internal casts. In these casts the beaks 

 are more erect than in specimens with the shell preserved and they 

 seem to be a little nearer the center of the shell. The muscular 

 impressions are large and prominent and are connected by the 

 well-defined pallial impression. 



Formation and locality. Manasquan marl, New Egypt and 

 Squankum (Whitfield). 



Geographic distribution. New Jersey. 



Genus SCAMBULA Conrad. 



Scambula perplana Conrad. 



Plate LXL, Figs. 13-14. 



1869. Scambula' perplana Con., Am. Jour. Conch., vol. 5, p. 48, 



pi. 9, figs. 7-8. 

 1872. Scabula perplana Con., Proc. Acad. Nat. Sci. Phil. 



(1872), p. 51, pi. i, fig. 2. 

 1886. Scambula perplana Whitf., Pal. N. J., vol. i (Monog. U. 



S. G. S., vol. 9), p. 123, pi. 1 8, figs. 8-10. 

 1905. Crassatellites (Scambula) perplanus Johns., Proc. Acad. 



Nat. Sci Phil. (1905), p. 14. 



