176 UNITED STATES GEOLOGICAL SURVEY OE THE TERRITORIES. 



P ro I oc a I'd ■ ;i (Lcploriiidisi) 1:1 in, L & S. isp.i. 



Plato 17. figs. J, a, b, c. 



Cardium varum, Evans ami Shnmard (1857), Trans. Acad. Sci. St. Louis, I, 39. 

 Cardium (Protoeardial) raram, Meek (1884), Smithsonian Check-List Cret. Fossils, 12. 



" Shell small, ovate-subquadrate, moderately gibbous, inequilateral; sub- 

 stance very thin, length and breadth nearly equal ; cardinal edge short, some- 

 what sharp ; beaks projecting above the cardinal margin, nearly medial, 

 rather blunt, incurved ; umbo oblique, somewhat gibbous, subangulated 

 behind ; buccal and pallial margins rounded; anal margin obliquely subtruu- 

 cated ; surface polished and marked with very tine, closely-arranged, concen- 

 tric lines, crossed on the posterior side by nearly obsolete longitudinal ribs, 

 becoming more prominent as they reach the border, which on this part of the 

 shell is finely crenulated." — (E. & S.) 



As suggested by Doctors Evans and Shnmard, this species resembles, in 

 its general form, their C. subquadratum ; but it is more polished, much 

 thinner, has less distinct radiating costs behind, and more prominent beaks. 

 Indeed, in our specimens, the radiating costie are generally entirely obsolete, 

 and the uinbonal region is always more gibbous than in ('. subquadratum ; 

 while its anal margin is more rounded in outline, and the valves not so com- 

 pressed behind the uinbonal slopes. In addition to these differences, the 

 posterior muscular impression in the species now under consideration is much 

 broader in proportion, and subquadrate instead of ovate. The pallial line is 

 waved into about two shallow sinuosities behind, as in C. subquadratum. 



Locality and posit ion. — On the Yellowstone River, 150 miles above its 

 mouth ; where it is very abundant in a bed containing a mingling of the forms 

 belonging to the Fox Hills and Fort Pierre groups. 



Protoca.rd.ia (Leptocardia!) pertenois, M. & H. 



Cardium pcrtenue, Meek and Hayden (1861), Proceed. Acad. Nat. Sci. Pliilad., XIII, 442. 



Shell small, very thin, vertically broad-sub- 

 ovate, its height being a little greater than its 

 breadth, very ventricose ; anterior and basal margins 

 rounding regularly together ; posterior margin a 

 Protocardu, pcriand.s, u. & H. little straightened and vertical near the middle. 

 Fig. 13. Right-side view. rounding to the hinge above and into the base 



Fig. 14. Au outline anterior view, 



to show convexity. below ; beaks elevated, ventricose, central, and 



Fig. 13. 



Fig. 14. 



