238 University Geological Survey of Kansas. 



proper location is with the Myliobatidse. The living members 

 of the family, the sea-devils, are broad, flat fishes, allied to the 

 rays, with a disk-like body. Many attain an enormous size, 

 fifteen or twenty feet in length, and weigh a thousand pounds 

 or more. In some the pectoral fins take on almost the charac- 

 ter of limbs, and are said to be used in scooping up their food 

 and transferring it to the mouth. The teeth are flat and pave- 

 ment-like, and are used for crushing crabs and shell-fish. The 

 fish are viviparous, and for the most part live in tropical or 

 semitropical waters. 



The teeth in Ptychodus are not less than 600 in number in 

 each jaw, at least in some species. They are arranged in par- 

 allel rows, decreasing in size from within outward, except that 

 in the supposedly upper jaws the median row is composed of 

 small, low and smooth teeth, very much unlike the immediately 

 adjacent ones. In P. mortoni there are eight rows on either 

 side of this median row, or seventeen in all. The lateral teeth 

 become more transversely elongated, the surface markings less 

 conspicuous, and the form more unsymmetrical. About fifteen 

 species of the genus have so far been discovered, all from the 

 Upper Cretaceous. One or two species, including our most 

 common one, have been discovered in both Europe and North 

 America, and it is not improbable that the identity of yet others 

 will be established when they are better known. The teeth vary 

 so much in size and shape in the same individual that the iden- 

 tification from single specimens is often impossible or a matter 

 of great uncertainty. 



Ptychodus mortoni. Plate XXV; plate XXVI, fig. 1; plate XXVII. 



Ptychodus mortoni (Mantell) Morton, Journ. Acad. Nat. Sci. Phil., viii, 

 p. 215, pi. x, f. 7; Agassiz, Poiss. Foss., in, p. 158, pi. xxv, ff. 1-3; Leidy, 

 Proc. Acad. Nat. Sci. Phil., (1868), p. 205; Ext. Vert. Fauna, p. 295, pi. 

 xvin, ff. 1-14; Cope, Cret. Vert., p. 294; Woodward, Quart. Journ. Geol. 

 Soc, xliii, p. 130; Cat. Foss. Fishes Brit. Mus., i, p. 159; Proc. Geol. 

 Assoc, xin, p. 191, pi. v, f. 4; Williston, Kans. Univ. Quart., ix, p. 30, pi. 

 vn, vin, f. 1, pi. ix — Alabama, Mississippi, Niobrara of Kansas, English 

 Chalk. 



This species is the most common one of this genus in the 

 Kansas Cretaceous, occurring only in the Niobrara beds, so far 

 as I am aware, and, for the most part at least, in the lower part 



