560 



NORTH AMERICAN INDEX FOSSILS. 



548. C. kummeli Weller. Cretacic. 



When found as internal molds it is like the molds of C. spill- 



mani in its long and slender form, but it is not usually so large, 



and lacks the radial ribs which are 

 usually impressed on the posterior 

 slope of those molds. 



Ripleyan of New Jersey (Nave- 

 sink-Tinton), Alabama, Mississippi. 

 549. C. meekianum Gabb. 



Pliocenic. 

 Large (over 2.5 inches in height), 

 oblique, with abruptly truncated 

 posterior end and prominent and 

 rounded anterior. Radiating ribs 

 about 22, absent from the posterior 

 slope, large and flattened on top. 

 Shell crossed by irregular lamellose 

 concentric lines which become tu- 

 bercles toward the beaks. 



Upper and Lower Pliocenic and possibly Miocenic of California. 



Fig. 767. Cardium tenuistriatum, 

 a more robust internal mold. (N. J. 

 Pal., I.) 



CLVIII. Protocardia Beyrich. 



Similar to Cardium but with radiating ribs only on posterior 

 portion of shell, the remainder covered with concentric ridges. No 

 lunule or escutcheon present. Comanchic-Recent. 



550. P. texana Conrad. (Fig. 768.) Comanchic. 

 Small to very large (over three inches long). 



Posterior fifth of shell covered with about fifteen 

 radiating ribs. 



Washita of Colorado, Texas (especially com- 

 mon in the Buda). 



551. P. subquadrata Evans and Shumard. 



Cretacic. 



Small (diameter less than .5 inch), more quad- 

 angular than P. lenis with posterior margin truncated 

 Radial ribs of posterior portion somewhat obscure. 



Montanan : North Dakota, South Dakota, Wyoming, Assini 

 boia, Saskatchewan. 



Fig. 768. Pro- 

 to car dia texana. 

 (After Shattuck). 



Gibbous. 



