544 CRETACEOUS PAI.EONTOLOGY. 



1862. Crassatella lineata Shum., Proc. Bost. Soc. Nat. Hist., 



vol. 8, p. 201. 

 1864. Crassatella monmouithensis Meek, Check List Inv. Foss. 



N. A., Cret. and Jur., p. 11. 

 1864. Venilia trapezoidea Meek, Check List Inv. Foss. N. A., 



Cret. and Jur., p. 13. 

 1868. Crassatella Monmouthensis Con., Cook's Geol. N. J., p. 



726. 

 1868. Venilia trapezoidea Con., Cook's Gaol. N. J., p. 727. 

 1876. Btea mowmouthewsis Con., Proc. Acad. Nat. Sci. Phil. 



(1876), p. 275. 

 1886. Crassatella Monmoutltensis Whitf., Pal. N. J., vol. i 



(Monog. U. S. G. S., vol. 9), p. 119, pi. 17, figs. 21-22. 

 1886. Veniella siuboiMlis Whitf., Pal. N. J., vol. i (Monog. U. 



S. G. S., vol. 9), p. 150, pi. 19, figs. 1-2. 

 1886. ^Veniella trapezoidea Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 151, pi. 19, fig. 3. 

 1905. Crassatellites monmouthensis Johns., Proc. Acad. Nat. 



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

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



(1905), p. 13. 

 1905. Veniella trapezoidea Johns., Proc. Acad. Nat." Sci. Phil. 



(1905), p. 13. 



Description. — ^The dimensions oi an average specimen are: 

 length, 26 mm. ; height, 18 mm. The specimens sometimes attain 

 a length of 30 mm. or more. Shell very oblique and inequilateral, 

 subtrapezoidal to subelliptical in outline, the beaks situated about 

 one-third the length of the shell from the anterior extremity. 

 Anterior margin rounding into the basal margin; basal margin 

 convex anteriorly and sometimes throughout, often somewhat 

 gibbous in the middle, and usually slightly sinuate posteriorly; 

 postero-basal extremity acutely subangular, posterior margin 

 obliquely truncate, the postero-dorsal margin straight or slightly 

 curved, sloping from the beak tO' the posterior hinge extremity, 

 where it meets the truncated posterior margin in an obtuse angle. 

 Valves with an angular or subcarinate umbonal ridge passing 

 from the beak to the postero-ventral extremity of the shell; in 



