INVERTEBRATE rAL^ONTOLOGY. 219 



Subgenus PROCARDIA, Meek. 

 I * h « > I a <l o ii i > a (Procardia) II o d g i i , M . 



Plate 13, figs. 3, a, b. 

 Isocardiaf 2odgii,Mcck (1871), Proceed. Acad. Nat. Sci. Philad., XXIII, 183. 



Shell cordate-subtrigonal, very gibbous and short, the length only about 

 equaling the height ; beaks elevated, gibbous, involuted, and placed over the 

 anterior margin ; posterior dorsal slope abrupt, with margins strongly 

 incurved, but not forming a false area; posterior extremity narrowly rounded 

 or subangular below, and apparently moderately gaping ; anterior side nearly 

 vertically and abruptly truncated from the beaks to the subangular anterior 

 basal extremity, and impressed or excavated so as to form a kind of large, 

 cordate, lunule-like area, extending with the curve of the beaks nearly to 

 their points; while within this there is a smaller, deeper, and more sharply- 

 defined lunule under the beaks-; basal margin forming a nearly semi -ovate 

 curve from the anterior basal angle to the posterior basal extremity. Sur- 

 face ornamented by small, nearly regular, radiating cost£e, that are not defined 

 on the anterior truncated end ; crossing these are broader, less distinct, con- 

 centric ridges, that become smaller and more defined on the truncated ante- 

 rior area. 



Length and height, each 1 inch ; convexity, 0.86 inch. 



This shell is so peculiar that I know of but a single species with which 

 it need be compared, that is, Cardium decussatum, Sowerby (= Pholadomya 

 decusmta, Ag. ?), from which it differs specifically in its smaller size and 

 much more slender and crowded radiating costse. 



I am under obligations to Dr. J. S. Newberry, the State geologist of 

 Ohio, for the use of the type specimen of this species. It was brought 

 from the Upper Missouri by Prof. J. T. Hodge, after whom I have named 

 the species. 



Locality and position. — Near the Great Bend of the Missouri, below Fort 

 Pierre; in the Fort Pierre group of the Cretaceous series of that region. 



