MOLLUSCA. 411 



1864. Area quindecemradiata Meek, Check List Inv. Foss. N. 



A., Cret. and Jur., p. 9. 

 1864. CucuUcEa transverscdis Meek, Check List Inv. Foss. N. 



A., Cret. and Jur., p. 8. 

 1864. Cibota multiradiata Meek, Check List Inv. Foss. N. A., 



Cret. and Jur. p. 9. 

 1868. Idonearca quindecemradiata Con., Cook's Geol. N. J., p. 



376, figure. 

 1868. Area altirostris Con., Cook's Geol. N. J., p. 725. 

 1868. Idonearea transversa Con., Cook's Geol. N. J., p. 725. 

 1868. Area ? quindeeemradiata Con., Cook's Geol. N. J., p. 725. 

 1886. Area altirostris Whitf., Pal. N. J., vol. i (Monog. U. S. 



G. S., vol. 9), p. 82, pi. 12, figs. 22-23. 

 1886. Trigonarca transversa Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 89, pi. 12, figs. 13-16. 

 1886. Cibota multiradiata Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 94, pi. II, figs. 21-22. 

 1886. Area quindeeemradiata Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 208, pi. 27, figs. 10-13. 

 1905. Area altirostris Johns., Proc. Acad. Nat. Sci. Phil., 



1905, p. 9. 

 1905. Area quindeeemradiata Johns., Proc. Acad. Nat. Sci. 



Phil., 1905, p. 9. 

 1905. Cucullcea gasbbi Johns., Proc. Acad. Nat. Sci. Phil., 1905, 



p. 8. 



Deseription. — Shell usually somewhat below medium size, the 

 dimensions of a rather small but nearly perfect internal cast 

 being : length, 22.5 mm. ; thickness, 23.5 mm. ; height, 22.5 mm. ; 

 length of hinge-line, 21.5 mm.; very inequilateral, the valves 

 ventricose, with prominent, projecting, distant and slightly in- 

 curved beaks in the internal casts, situated in front of the mid- 

 length of the shell and a little in front of the mid-length of the 

 hinge-line. Anterior margin rounding rapidly backward from 

 the anterior extremity of the hinge-line and passing without in- 

 terruption into the broadly rounded basal margin ; postero-basal 

 extremity sharply rounded or subangular, situated below the mid- 

 height of the shell ; posterior margin obliquely truncate, meeting 



