30 KANSAS UNIVERSITY QUARTERLY. 



broad, flat fishes, allied to the rays, with a disk-like body. Many at- 

 tain 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 character of limbs, and are said to be used in scooj^ing 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. They are 

 viviparous, and for the most part live in tropical or semitropical 

 waters. 



The teeth in Ptychodus are not less than 500 in number ia each 

 jaw, at least in some species. They are arranged in parallel rows, de- 

 creasing 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. mor- 

 toiii there are eight rows on either side of this median row, or seven- 

 teen in all. The lateral teeth become more transversely elongated, 

 the surface markings less conspicuous, and the form more unsymmet- 

 rical. 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 identification from 

 single specimens is often impossible or a matter of great uncertainty. 



rtyehodns inoitouL Plate VII; plate VIII, fig. 1: plate IX. 



Pfyehnrhifi ?>ior<orr/ ( Mantel] ) Morton, Journ. Acad. Nat. Sci. Phil. VIII, 215, 

 pi. X, f. 7: Aga.ssiz, Poiss. Foss. Ill, 158, pi. XXV, ff. 1-3: Leidv, Proc. 

 Acad. Nat. Sci. Phil. 1868, 205: Ext. Vert. Fauna, 295, pi. XVIII, ff. 1-11: 

 Cope, Cret. Vert. 291; Woodward, Quart. Journ. Geol. Soc. XLIII, 130; 

 Cat. Foss. Fishes Brit. Mus. I, 159; Proc. Geol. Assoc. XIII, 191, pi. V, 

 f. 4 — Alabama, Mississippi, Niobrara of Kansas, English Chalk. 



This species is the most common one of this genus in the Kan.sas 

 Cretaceous, occurring only in the Niobrara beds, so far as I am aware ,^ 

 and, for the most part at least, in the lower part of the beds. I have 

 before me at the present time two excellent series of teeth of this 

 species; one, including about eighty teeth, obtained from the estate 

 of the late Joseph Savage ; the other collected in the vicinity of 

 Castle Rock, in Trego county, by Prof. E. S. Rose — an exceedingly 

 interesting specimen, because most of the teeth are in place in the 

 matrix. A number of the teeth of the Savage specimen have been 

 arranged serially and photographed in plate VII. Of course the ar- 

 rangement is not the natural one, but the plate will show in an excel- 

 lent way many of the characters of the teeth better than they can be 

 described. In plates VIII and IX are given three views of portions 

 of the Rose specimen; that of plate VIII (fig. 1) shows a little more 

 than one-half of the upper view. One end (the left of the figure) has 



