Williston.] Cretaceous Fishes. 245 



the way to the apex : root narrow, apparently not at all pro- 

 duced at the angles ; thinned and not at all tumid. 



Type Xo. 1949, U. S. National Museum. (Jreenleaf sandstone 

 at Greenleaf ranch. 



Height of middle cusp 7 mm. 



Width of same at base 4 " 



Height of denticles -I " 



Width of same 2\ " 



Scylliorhinus planidens. Plate XXIV, fig. 7. 



Scyllium planidens Williston, Kans. Univ. Quart., jx, p. 35. 



Central cusp broad, pointed, convex from side to side, with 

 sharp, non-crenulate edges ; lateral cusps sharply pointed, 

 smooth, two in number; root thin, narrow, moderately pro- 

 duced below the posterior denticle, smooth. 



Height of mediau cusp 4 mm. 



Width of same at base I) " 



Width of base of tooth G " 



Height of denticles 1\ " 



Type Xo. 1949, U. S. National Museum. From same horizon 

 as the preceding species. 



I refer provisionally to this species numerous other speci- 

 mens from the same horizon and collection. They differ in the 

 relative size of the denticles, the more posterior direction of the 

 main cusp, and the size. One tooth seems to lack the anterior 

 denticle, which is always the smaller of the two ; its absence 

 may be due to injury. 



Scylliorhinus I Lamna? I gracilis. Plate XXIV, fig. 6. 



Scyllium {Lamnat) gracilis Williston, Kans. Univ. Quart., ix, p. •">•">. 



Main cusp elongate, slender ; inner surface smooth, gently 

 convex longitudinally, more so transversely, with sharp, smooth 

 edges ; the interior edge nearly straight, the posterior somewhat 

 concave ; denticles of nearly equal size, small, slender, acute ; 

 base narrow, prolonged into a slender root at each extremity. 



Height of tooth 9 mm. 



Length of middle cusp G " 



Width of same at base 3 " 



Length of denticles 2 " 



One specimen, No. 1949, [], S. National Museum, with the 

 preceding species. 



