t903-] 



Hay\ North American Cretaceous Fishes. 



6i 



the symphyseal surface of the dentary of P . latinieiitum is 

 very distinct in specimens which on account of the small 

 height of the coronoid process would have to be assigned to 

 P. caiiinits. The height of the coronoid process will, with 

 little doubt, be found to vary in all degrees between the 

 measurements given by Cope for his two species. 



The mandible of the species (Fig. 44) appears to have had 

 an external vertical surface and an inferior nearly horizontal 

 surface. In some specimens these are separated by a sharp 

 ridge; in others they are with difficulty distinguishable, a 

 condition probably due to distortion during fossilization. 

 Similarly, the maxilla has presented an external nearly flat 

 surface separated by a sharp border from a flat superior sur- 

 face. This surface, again, meets a fiat palatal surface at a 

 sharp internal, or mesial, border. The section of the maxilla 



Fig. 44. Pachyrhizodus caninus Co^e. No. 1662. X 3. Mandible, d//^., angular ; «r^., 

 articular ; den., dentary. 



is, therefore, nearly triangular. In one specimen, however, 

 the maxilla of one side has the form described, while the other 

 is so distorted that its section is nearly parallelogrammic. 

 These modifications are mentioned in order to show the 

 necessity of guarding against giving too much value to varia- 

 tions in the forms of the bones of this genus. 



Of the palatines and the pterygoids of this species the 

 writer has been able to learn little. Loomis {op. cit., pi. 

 xxvii, fig. 12) has figured what he regards as a palatine, but 

 it seems to be identical with a left maxilla in this Museum's col- 

 lection. Besides, one would hardly expect to find a palatine 

 of a length so great that it would reach nearly to the quadrate. 



In the National Museum at Washington there is a speci- 

 men of this species which I have been permitted to study. 



