246 University Geological Survey of Kansas. 



LAMNIDJE. 



The Lamnidse comprise the largest and most voracious of the 

 sharks, represented by a number of species in the oceans of the 

 present time. They are elongated fishes, the dorsal fin without 

 spine ; there is no nictitating membrane to the eye, and the gill 

 openings are wide. The teeth are solid in the adult, and are 

 300 or more in number. The teeth are found very commonly 

 in the Cretaceous deposits of Kansas, as elsewhere, usually 

 scattered singly, though occasionally found more or less con- 

 nected by the calcified cartilage of the jaws in several rows. 

 Owing to the great variation of size and shape of the teeth in 

 the same individual, it is often difficult or impossible to cor- 

 rectly determine the forms. Doctor Eastman has recently fig- 

 ured and described the nearly complete dentition of Isurus 

 mantelli, the most common species of the family in Kansas. 

 Doubtless similar variations will be found in the different spe- 

 cies of the other genera of this family. 



ISURUS. 



This genus differs from Lamna only in the prevailing absence 

 of the lateral denticles of the teeth. The teeth are large. The 

 genus occurs from Jurassic to the present time. 



Isurus mantelli. Plate XXXI, figs. 11-46; plate XXXII, figs. 2-2m. 



Oxyrhina mantelli (Geinitz) Agassiz, Poiss. Foss., in, p. 282, pi. xxxin, 

 if. 1-5, 7-9; Eastman, Paleontographica, xli, pp. 149-192, pll. xvi-xviii 

 (where additional extensive synonymy will be found); Woodward, Proc. 

 Geol. Assoc, xm, p. 196 — Cenomanian, Senonian and Turonian of Eu- 

 rope; Kansas, Texas, New Jersey, Alabama, Colorado, etc. 



Oxyrhina extenta Leidy, Ext. Vert. Fauna, p. 302, pi. xvin, ff. 21-25. 



"Moderate-sized, stout, three-cornered teeth; the crown on 

 the outer side nearly flat, with one or more vertical wrinkles ; 

 on the inner side, lightly convex and smooth ; root long, thick, 

 low, moderately deeply furcate, usually obtuse at the ends, and 

 on both sides more or less flattened." 5 



This species is very common in the Kansas Niobrara, in fact, 



5. Eastman, 1. c. 



