INVEUTEnUATE l'A L.EONTOLIH! Y. 17.*) 



Subgenus LEPTOCARDIA, M. 



Section (o). 



Protocardiii (Leptocardia) subquadra.ta, E. & S. (sp.). 



Plate 29, figs. S,a,b,c,d,e. 



Card in m s ii hqiiwl rut ii in, Evans and Shumard (1857), Trans. Acad. Sci. St. Louis, I, 39. 

 Cardium (Protocardia .') subquadratnm, Meek (18(34), Smithsonian Cheek-List Cret. Fossils, lrs. 



"Shell small, subquadrangular, length greater than the height, gibbous; 

 anterior margin rounded, posterior margin truncated, very slightly arched ; 

 umbones prominent, large, obtusely subangulated ; beaks nearly medial, 

 rather obtuse, and extending but little beyond the cardinal margin ; substance 

 of the shell thin ; surface with fine concentric striae of growth, waved and 

 dentate posteriorly, where they are crossed by obscure longitudinal ribs. 



" Length, 54 lines ; height, 4| lines ; thickness, nearly 4 lines." — 

 (E. & S.) 



Of this species, we have a number of very well preserved specimens, 

 some of which show the hinge and other internal characters quite as well as 

 they can be ^een in a recent shell. The cardinal teeth are small and rather 

 unequal, the posterior one in the right valve, and the anterior one in the left, 

 Being larger than the other. The lateral teeth are compressed, and also 

 small ; the anterior one in each valve being a little more prominent than the 

 posterior. 



Both muscular impressions are ovate and nearly of the same size ; while 

 the pallial line, which is quite distinct, instead of having one well-defined 

 sinus, is merely waved behind, so as to form two faint sinuosities. The 

 postero-ventral margins are rather distinctly crenulated within ; the crenula- 

 tions corresponding to the obscure radiating costag of the posterior side, 

 which do not extend forward quite to the middle of the base. These costa3 

 are generally rather obscure, and on some individuals they are nearly or quite 

 obsolete. The posterior umbonal slopes are quite prominently rounded, and 

 just behind them the valves are rather abruptly compressed, so as to form an 

 undefined groove, which extends from the back part of the beaks obliquely 

 backward and downward. 



Locality and position. — Moreau River. Long Lake, Fox Hills, &c. ; from 

 the Fox Hills group, or formation No. 5 of the Upper Mo. Cretaceous. 



