464 CRETACEOUS PALEONTOLOGY. 



above description has been made. Whitfield's material from 

 which he illustrated the species was much more incomplete than 

 that now available, some of his figures are more or less restored, 

 and none of them represent the characters of the species as 

 ordinarily preserved in the New Jersey faunas. The internal 

 casts do not preserve the characters of the upper portion of the 

 shell which are really the most essential specific features, but 

 the presence of the keel-like extension of the shell along the 

 hinge-line, rather than a sharply inflected border to form a broad 

 escutcheon, can usually be recognized. 



The impression from which Whitfield took the cast used to 

 illustrate Gouldia paratts Con., is quite certainly the impression 

 of a portion of a Trigonia shell, probably a member of this 

 species. 



Formation and locality. Merchantville clay-marl, near Mat- 

 awan (101), Lenola (163); Woodbury clay, near Matawan 

 (103), near Haddonfield (183) ; Wenonah sand, near Marlboro 

 (130), near Crawfords Corner (i26 3 ). 



Geographic distribution. New Jersey, Alabama, Mississippi, 

 Texas. 



Trigonia cerulia Whitfield. 

 Plate XL VIII., Fig. 13. 



1886. Trigonia cerulia Whitf., Pal. N. J., vol. i (Monog. U. S. 

 G. S., vol. 9), p. 114, pi. 14, fig. 7. 



Description. Shell small, the dimensions of an averaged sized 

 left valve being: length, 30 mm.; height, 24.5 mm.; convexity, 

 9 mm. Subovate in outline, the beaks nearly anterior, obtuse, 

 scarcely recurved. Anterior and ventral margins together form- 

 ing nearly a semicircle, posterior margin rather sharply rounded 

 above into the dorsal margin ; dorsal margin gently concave from 

 the beak to the posterior extremity of the hinge-line. Surface 

 of the valve divided into two portions by an obscure ridge, sub- 

 parallel with the dorsal margin, passing from the posterior side 

 of the beak, with a gently concave curvature to the posterior mar- 



