174 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Subgenus PROTOCARDIA. 

 Pro tocardi :■ Salinacnsis, Meek. 



Plate 2, figs. 13, a, b, c. 



Cardium ( Protocardiu) Salinaense, Meek (1871), Hayden's Second Report Geological Survey of the Terri- 

 tories, 30G. 



Shell small, nearly orbicular, very slightly longer than high, rather 

 gibbous; pallial margin forming a semicircular curve; anterior margin 

 rounded, the most prominent part being at, or a little above, the middle, 

 while, below this it usually rounds off somewhat obliquely into the base; 

 posterior margin broader, and sometimes slightly subtruncated, or merely 

 broadly rounded ; beaks rather depressed, convex, incurved, slightly in 

 advance of the middle ; dorsal outline sloping more abruptly in front than 

 behind ; posterior umbonal slopes not prominent. Surface ornamented on 

 the sides and front by comparatively . rather large, rounded, very regular 

 concentric costee, sepai'ated by smaller furrows ; while sixteen to twenty 

 smaller radiating cosia\ roughened by very regular little vaulted prominences, 

 formed by the marks of growth, occupy the posterior region of each valve. 



Height, 0.66 inch ; length, 0.68 inch ; convexity, about 0.49 inch 



This little shell is allied somewhat to Cardium peregrinum, d'Orbigny, 

 and C. Hillanum, Sowerby. It is much smaller, however, than the latter, 

 and has a different outline, not being so truncated behind, nor so regularly 

 rounded anteriorly; while its concentric costa' are proportionally much larger 

 and less numerous, and its radiating costse are more roughened. In the 

 latter character, it agrees more nearly with C. peregrinum. It, also differs 

 from the latter, however, in having proportionally much larger concentric 

 costse ; and its radiating ribs are straighter, and occupy larger area of the 

 valves. Its anterior outline is likewise less broadly and regularly rounded 

 than in d'Orbigny's species. 



Locality and position. — Twelve miles southwest of Salina, Kansas; 

 Dakota group of the Upper Missouri Cretaceous series. Collected by Prof! 

 B. F. Mudge. 



