MOLLUSCA. 537 



Veniella trigona (Gabb). 



Plate LIX., Figs. 1-3. 

 1 86 1. Venilia trigona Gabb, Proc. Acad. Nat. Sci. Phil. (1861), 



P- 324- 

 1864. Venilia trigona Meek, Check List. Inv. Foss. N. A., Cret. 



and Jur., p. 13. 



1868. Venilia trigona Con., Cook's Geol. N. J., p. 727. 

 1886. Veniella trigona Whitf., Pal. N. J., vol. I (Monog. U. S. 



G. S., vol. 9), p. 149, pi. 19, figs. 11-14. 

 1905. Veniella trigona Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 13. 



Description. The dimensions of a nearly complete left valve 

 are: length, 58 mm.; height, 51 mm.; convexity, 25 mm. 

 Shell subtrigonal in outline. Hinge-line strongly curved; an- 

 terior margin sharply rounding into the basal margin; basal 

 margin convex in front, becoming straight or slightly concave 

 posteriorly; postero-basal extremity angular; posterior margin 

 truncate, rounding above into the long, convex post-cardinal 

 margin. Valves very ventricose with a sharply angular, strongly 

 curved umbonal ridge. Beaks extending as far forward as the 

 anterior margin of the shell, strongly incurved. Post-umbonal 

 slope abrupt, becoming less so posteriorly, divided by an obtusely 

 subangular ridge which originates back of the beak and describes 

 a curve to the post-cardinal extremity; the area between the 

 umbonal and cardinal ridges is slightly concave, and is much 

 broader than the area between the cardinal ridge and the cardinal 

 margin. Anterior slope with a slight sinuosity just in front of 

 the umbonal ridge in the lower portion of the shell; in front of 

 this the surface is convex, becoming more abrupt anteriorly and 

 being somewhat inflected to the antero-cardinal margin beneath 

 the beak. Shell substance very thick. Surface of the shell 

 rugosely marked with irregular concentric lines of growth and 

 with rather broad, wrinkle-like ridges; towards the beak there 

 is some evidence of two or more lamellar ridges as in V. conradi. 

 The strong rugosities do not extend across the post-cardinal 

 slope of the shell, this portion being marked only by the irregular 

 lines of growth. In the casts the beaks are straighter, much less 



