NATURAL SCIENCES OF PHILADELPHIA. 205 



Dr. D. G. Brinton was elected a member. 



On favorable report of the Committee, the paper of Dr. Leidy, 

 presented Sept. 15th, entitled " Extinct Mammalia of Dakota and 

 Nebraska," etc., reported in favor of its publication in the Journal. 



On favorable report of the Committees, the following papers were 

 ordered to be printed : 



Notice of American Species of FTYCHODTJS. 



BY JOSEPH LEIDY, M. D. 



The Cestraciont genus of fishes Ptychodus, so far as known, is confined to 

 the Cretaceous Formations. Remains, consisting of teeth, I have had the 

 opportunity of inspecting from Ahxbama, Mississippi and Kansas, and 

 although reported to exist in the Cretaceous Formation of Delaware, I have 

 not met with them from that locality nor from the Green Sand, of correspond- 

 ing age, of New Jersey. The following list comprises all the specimens of 

 American Ptychodus teeth I have had the opportunity of examining. 



Ptychodus Mortoni. 



Agassiz, Poissons Fossiles III. (1833-43), 158, Tab. 25, figs. 1 — 3; copied in 

 figs. 773, 773a, of Dana's Manual of Geology. 



Palate bone of a fish ? Morton : Syn. Org. Rem. Cret. Group. (1834), pi. 

 xviii, figs. 1, 2. 



The teeth of Ptychodus Mortoni I have seen only from the cretaceous forma- 

 tion of Alabama and Mississippi. Morton, in the work above noticed, figures 

 a tooth, but does not mention the locality from which it was obtained. 



Agassiz, in his Poissons Fossiles, gives a good representation of a tooth of 

 this species, from the Green Sand of America, in three views, figs 1 — 3, Tab. 25. 



Dixon, in his Geology of Sussex, represents two small teeth, (figs. 6, 7, pi. 

 xxi), Avhich he refers to the same species. Though exhibiting some resem- 

 blance in character to the American teeth, I think a further comparison is 

 necessary to establish their specific identity. 



The teeth of Ptychodus Mortoni are well defined in character, and in com- 

 parison with teeth of well recognized European species are almost generic in 

 their peculiarity. Though exhibiting some varietj^, their likeness presents a 

 distinct specific uniformity. Their size of course varies greatly with age and 

 the relative position they occupied with one another in the mouth of the 

 fish. 



Viewed from above, the crown is reniform in outline, the long diameter being 

 transverse ; the incurvature posterior. The crown rises in the form of a cone 

 with a more or less obtuse summit. The sides of the crown slope to the base 

 and frequently more or less abrupt^ expand, laterally approaching the latter. 

 The back part is occupied by a wide triangular sinus for the reception of the 

 fore-part of the crown of the tooth which was situated in front of it when 

 the teeth were contained within the mouth. The border of the crown is thick 

 and rounded and dips beneath. At the sinus it is prominent. The summit of 

 the crown presents a prominent crucial ridge, more or less distinct in different 

 specimens. From the cross numerous ridges of about the same thickness 

 diverge upon the sides of the cone, branching in their course, multiplying and 

 becoming finer, and ultimately conjoining upon the base in a fine reticulation 

 extending to the borders of the crown. The coarser I'idges vary in their pro- 

 portionate length in different specimens. The reticulation of the base is most 

 extensive laterally, occupying usually half the breadth of the space between 

 the summit and border. It also occupies the sinus, and is least developed at 

 the fore-part of the crown. The width of the crowu approaches double the 



1868.] 



