WILLISTON : FISH TEETH FROM KANSAS CRETACEOUS. 31 



been folded underneath obliquely. Thi.s folded end is shown in plate 

 IX, fig. 1. Figure 2 of the same plate gives a view of a transverse 

 series, as arranged from the loose teeth taken from the right end of 

 the specimen — the one that protruded from the chalk when discovered. 

 About 480 teeth, all told, were obtained, and doubtless not a few had 

 been lost before the specimen was discovered. The set is referred to 

 the upper jaw, on the supposition of Woodward that the small me- 

 dian teeth belong in this jaw. 



Not a trace of osseous substance is preserved in the specimen. 

 The cartilage of the sharks' jaws is often preserved in a soft, calcified 

 condition, but it is evident that the material in which the teeth of 

 Ptychodus were lodged was of a more perishable nature, accounting 

 doubtless for the fact that Ptychodus teeth are so rarely found asso- 

 ciated. 



The teeth of this species differ markedly from those of all other 

 known species in having the center of the crown raised into a conical 

 apex, the summit of which is crossed by a short transverse ridge from 

 which other diverging ridges run. In the smaller lateral teeth these 

 ridges become less well marked and occupy a relatively smaller space, 

 becoming almost obsolete in the fifth row. The marginal area is 

 formed of fine reticulations in many of the larger teeth, though in 

 most of these and in all the smaller teeth the markings are more like a 

 fine punctulation, clearly visible only with the aid of a lens, giving a 

 uniform, finely roughened apjDearance. The median upper row is 

 composed of low, flattened teeth, transversely oval or subquadrate in 

 shape, with a slight elevation in the middle, and finely roughened 

 throughout the whole coronal surface, there being only the slightest 

 trace of the divergent ridges on the summit of the elevation. This 

 does not quite agree with Woodward's description of these teeth, in 

 which he states that they are " not marked with the radiating ridges, 

 but exhibit a minute smooth eminence in the middle of the crown." 

 Possibly this effect is due to wear. 



I*ff/c7iO(Ius poli/f/;/riis. Plate XI, fig. 9; plate X, fig. 14:. 



Ptycliodus pnluqijriia (Ruckland) Agassiz, Poiss. Foss. Ill, 156, pi. XXV, fF. 



'4-11, pi. XXV/^ ff. 21-23; Gibbes, Journ. Acad. Nat. Sci. Phil. I, 299, pi. 



II, ff. 5, 6 : Leidy, Proc. Acad. Nat. Sci. Phil. 1868, p. 208 : Cope, Cret. Vert. 



294; Woodward, Cat. Foss. Fishes Brit. Mus. I, 143, pi. V, f. T^Senoniac, 



Turonian of Europe, Rotten Limestone of Alabama, Niobrara of Kansas. 

 ? Ptychodus latissimus Agassiz, 1. c, fig. 8: Dixon, Foss. Sussex, pi. XXX, 



ff. 1, 2. 



A single tooth of very large size from the lower beds of the Nio- 

 brara Cretaceous of the Smoky Hill river is referred to this species 

 provisionally. Until numerous specimens are examined there can be 

 no certainty of its correct location, though the resemblances are suffi- 



