4 8o NORTH AMERICAN INDEX FOSSILS. 



Umbonal slope with 5 to 8 (or more) coarse, rounded, rather 

 irregular folds or plications, which become obsolete in the last 

 built portion of the shell. 



Bear River beds of Wyoming, etc. 



310. U. subspatulatus Meek and Hayden. Cretacic. 

 Surface as of U. vetustiis but differing from that species in more 



arched hinge line, more anterior beak, straight base and general 

 proportions. 



Judith River beds of Montana, Assiniboia. 



311. U. danae Meek and Hayden. (Fig. 640,/, £\) Cretacic. 

 Similar to U. subspatulatus in size and form but its convexity is 



greater, the beaks not so anterior, and it is unsculptured. 



Alberta (Lower Belly River), Montana and Assiniboia (Judith 

 River) ; also Lower Laramie of Wyoming and Alberta. 



312. U. senectus White. (Fig. 640, k.) Cretacic. 

 Thin. Cardinal and lateral teeth separated by a considerable 



space. Posterior to the line running from the beak to the pos- 

 terior basal angle the surface has numerous small crenulated un- 

 dulations. In front of this the surface is marked only with growth 

 lines. 



Montana (Judith River), Assiniboia (Lower Belly River) ; also 

 Laramie of Alberta. 



313. U. holmesianus. (Fig. 640, i, j.) Cretacic. 

 Basal (latest built) portion of shell marked with only concentric 



growth lines ; the rest of the shell covered with radiating costae 

 of close-set rhombic papillae. A strong medial sinus present. 

 Laramie : Wyoming, Utah. 



LXXXVII. Anodonta Cuvier. 

 Shell like Unio externally but usually much thinner and 

 smoother. Hinge without teeth. Fresh water. Cretacic- 

 Recent. 



314. A. propatoris White. Cretacic. 

 Elongate, subelliptical, moderately convex. Beaks small, 



slightly elevated above the hinge line. Hinge line long, straight. 

 Ventral border broadly convex ; front regularly rounded from the 

 base to the antero-dorsal border which is more abruptly rounded 

 to the hinge line. Postero-dorsal border oblique and slightly 



