592 CRETACEOUS PAEEONTO^LOGY. 



t886. Cardium (Criocardiwrn) dmnosum Whitf., Pal. N. J., 

 vol. I (Monog. U. S. G. S., vol. 9), p. 133, pi. 20, 

 figs. 1012, not figs. 9 and ? 13. (Not C. durmoswm 

 Conrad. ) 



1886. Cardium, (Criocardium) multiradiatum Whitf., Pal. N. 

 N. J., vol. I (Monog. U. S. G. S., vol 9), p. 135, pi. 

 21, figs. 1-3. (Not C. multiradiatum Gabb.) 



1886. Fragum tenuistriaium Whitf., Pal. N. J., vol i (Monog. 

 U. S. G. S., vol. 9), p. 139, pi. 20, figs. 15-16. 



Description. — The dimensions of an internal cast are: height, 

 44 mm. ; width, 37 mm. ; thickness, 35 mm. Earge examples 

 sometimes attain a height of over 60 mm. Shell irregularly 

 subovate in lateral view and cordate in end view. Hinge-line 

 arcuate; anterior and basal margins, from the extremity of the 

 hinge-line to the middle of the basal margin, describing a nearly 

 regular, arcuate curve; posteroi-basal margin curving more 

 sharply around the postero^basal extremity of the shell into the 

 posterior margin; posterior margin much straighter than the 

 anterior, usually gently convex but sometimes nearly or quite 

 straight. Beaks situated at about the middle of the hinge-line, 

 rather prominent, elevated, pointed and incurved, considerably 

 more prominent in the casts than in the specimens with the shell 

 preserved. Valves gibbous, most prominent, but not angular, 

 along a line from the beaks tO' the posteroi-basal extremity, the 

 posterior slope more abrupt than the anterior. Muscular im- 

 pressions rather large, the posterior ones scarcely impressed and 

 often scarcely distinguishable upon the casts; the anterior ones 

 more strongly impressed. Each valve with a strong, somewhat 

 curved cardinal tooth beneath the beak, with a pit for the re- 

 ception of the tooth of the opposite valve; in each valve is a 

 single anterior and posterior, rather strong, lateral tooth, some- 

 what remote but nearly equidistant from the cardinal tooth. 

 The inner free margin of the valves is crenate. Externally the 

 shell is marked by flat, radiating costse wider than the inter- 

 spaces; from the interspaces rise rows of laterally compressed 

 spinules or tubercles which are longer and stronger upon the 



