VTilliston.] Cretaceous Fishes. 239 



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. G. E. Rose — an exceedingly interesting specimen, be- 

 cause 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 XXV. Of course the arrangement 

 is not the natural one, but the plate will show in an excellent 

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

 be described. In plates XXVI and XXVII are given three 

 views of portions of the Rose specimen: that of plate XXVI 

 (fig. 1) shows a little more than one-half of the upper view. 

 One end (the left of the figure) has been folded underneath 

 obliquely. This folded end is shown in plate XXVIII, 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 discov- 

 ered. About 550 teeth, all told, have been obtained, and doubt- 

 less 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 median teeth belong in this jaw. 



Xot 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 associated. 



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 reticula- 

 tions in many of the larger teeth, though in most of these and 

 in all the smaller teeth the markings are more like a fine punc- 



