Williston.] Cretaceous Fishes. 253 



C. pristodontus and C. lindstromi, both of which seem to be im- 

 perfectly differentiated from C.falcatus at present. 



In plate X X XIII, tigs. 1-1/, are shown a number of teeth per- 

 taining to a single individual and found associated with many 

 others, by Mr. Martin, in the Niobrara Cretaceous of the Smoky 

 Hill valley. Isolated teeth of this species are the most abun- 

 dant of the selachian teeth in the Niobrara of Kansas. Only in 

 very few instances have many teeth been found associated, so 

 that it is yet impossible to fully understand the dentition. The 

 species occurs rarely, if at all, in the lower Niobrara horizons, 

 where those of Tsurus and Ptychodus are the most abundant. 



Corax curvatus, u. sp. Plate XXX, figs. 7, 8. 



Two specimens from the same block which yielded those of 

 Ptychodus janeioayii and Lamna species, antea, seem evidently 

 specifically distinct from the foregoing. These teeth, while not 

 differing much in outline from certain ones referred to C. falca- 

 tus, show a marked variance in structure. In C.falcatus the 

 outer surface of the tooth stands out but very slightly. In C. 

 curvatus the crown is attached to the root very obliquely, so that 

 when resting upon a plane the tooth forms a high arch, touch- 

 ing only by the extreme tips of the roots and crown. The inner 

 surface, also, is very much more uneven and convex, the crown 

 separated from the root by a marked, narrow, transverse ridge, 

 which is scarcely indicated in the teeth of C.falcatus. Altitude, 

 8 mm. ; greatest width, 14 mm. ; horizon, lower or lowermost 

 Kenton of Ellsworth county. 



LEPTOSTYRAX. 



Williston, Kan-. Univ. Quart., IX. p. 12. 1900. 



Leptostyrax bicuspidatus. Plate XXIV, figs. 15, 15a; plate XXVI, fig. 7. 

 Leptostyraz bicuspidatus Williston, cf. cit. 42. 



Principal cusp long and -louder, flattened upon the outer 

 side, with sharp, smooth edges and a median convexity in the 

 middle of the flattened surface ; for the most part convex lon- 

 gitudinally, gently concave before the apex. Inner surface 

 strongly convex from side to side, concave on the lower half 



