226 



bone ; their apices rise a little above the edge of the external alveolar border. 

 The bases of the crowns are oval, and they display an anterior cutting-edge, 

 which descends from the apex, thus differing materially from those of the 

 P. caninus. The teeth diminish in size from the middle of the dentary bone 

 to the symphysis ; besides the latter are two teeth of reduced size. The outer 

 face of the dentary is smooth, except some small impressed fossae. The 

 mental foramina are small, and do not issue in a groove. Below them, on the 

 outer face, is a fossa, with level floor to the inferior margin. 



Measurements. 



M. 



Length of tho margin bearing four teeth 0.050 



Depth of the ramus at the third tooth 0. 025 



Elo vation of tho tooth-basis 0. 008 



Long diameter of tho baso of the crown on tho same 0. 00G 



STRATODUS, Cope. 



This genus is well characterized by its dentition, which is remarkable 

 for the small size and large number of the teeth, and their peculiar form. I 

 possess one premaxillary, a considerable part of the maxillary, and nearly the 

 whole of both palatines, besides other bones, of one species. I have, unfor- 

 tunately, no dentary bone of Stratodus. The outer row of palatines resem- 

 bles, in some measure, those figured in Cimolichthys levesiensis, Leidy, by 

 Agassiz. 



The premaxillary teeth are in two series. They are stout at the base 

 and oval in section, and are contracted and flattened rapidly upward. On 

 this basis is set an oval, sharp-edged, flat, or spade-shaped crown; the long axis 

 of compression being placed at right angles to that of the compression of the 

 apex of the base. This gives a barbed appearance. The maxillary teeth are 

 similar in form, but are in but few rows. The palatine teeth are constructed 

 on the same plan, but they are longer, ami the bases are subcylindric and 

 slightly curved. All the teeth possess a large pulp-cavity. 



The premaxillary bone displays some of the density of composition seen 

 in Ettrfwdus. Its upper anterior surface meets the inferior at an acute angle 

 It is a broad oval, and is slightly concave. The inner face forms a truncate 

 rim round the bases of the inner teeth, and terminates in a vertical crest of 

 dense bone. The external tace is, on the other hand, perpendicular, and 

 extends obliquely upward and backward. An acute anterior angle of the 

 maxillary underrnns it below, so far as to exclude all but one or two of the 



