1903.] H^y\ J^^orth American Cretaceous Fishes. 29 



Aiwgniiits, as represented by -4. aratiis and .4. javirostris, 

 described on succeeding pages, has the premaxillae free from 

 the ethmoid, and possibly from each other, and the dental 

 plates are deeply pitted. The lower plate is composed of 

 two and possibly of three median bones. 



Syntegmodiis is described as having the parasphenoid and 

 some other bones of the mouth covered with a thick mass of 

 osteodentine. This is penetrated by large canals which pass 

 from the surface to the bone on which the supposed osteo- 

 dentine mass rests. This mass is probably composed of 

 dense bone. On comparing Dr. Loomis's Syutegmodus, and 

 the known remains of .4. aratiis and ^4. javirostris and a 

 specimen resembling Syntcguiodiis alius, among one another, 

 it is difficult to see how they may be distinguished generically. 



Thryptodus is regarded by Dr. Loomis as having the 

 premaxillae not free, but probably consolidated with the eth- 

 moid. The parasphenoid has developed a great oval, con- 

 cave, dental plate, which is furnished with pits; while the 

 median bones of the floor of the mouth support plates which 

 work against the parasphenoidal plate. A study of the type 

 of Cope's Anogmius aratiis, figures of which are presented in 

 this paper, have convinced me that the relation of the pre- 

 maxillae to the ethmoid has been misunderstood by both Prof. 

 Cope and Dr. Loomis, and that Thryptodiis is identical with 

 the type of Anogmius aratus. In this form, as illustrated by 

 the types of A. aratus and Thryptodiis, the premaxillae appear 

 to be united, while in A. javirostris they are possibly, but not 

 certainly, free from each other. If this difference is confirmed 

 by other specimens it may require that two genera shall be 

 recognized; but for the present it seems to the author best 

 to unite all under Anogmitis. Pseiidothryptodus, with free 

 premaxillae, will be included. 



Reference has already been made to the difi'erences sup- 

 posed to exist between the vertebras of Pachyrhizodiis and 

 Anogmius . However much they may resemble, there is great 

 difference in the structure of the tails of the two genera. 

 There is apparently little difference in the form of the tail 

 fins, both being deeply forked. In Pachyrhizodiis, as shown 



