Stewart.] Cretaceous Fishes, 267 



Xiphactinus mudgei Cope, Niobrara Cretaceous, western Kansas. 

 Xiphactinus lowii Stewart, Fort Benton Cretaceous, central Kansas. 

 Xtphactinus brachygnathus Stewart, Niobrara Cretaceous, central Kansas. 



In a paper recently published by Professor Hay, of the United 

 States National Museum,- the author recognizes two more spe- 

 cies, X . molossus and X. thaumas, not mentioned in the list given 

 above, and says that it is quite probable that X. audax is the 

 same as some one of Professor Cope's species of Portheus. He 

 also recognized the great variation in the size and arrangement 

 of the teeth, but thought that the two species could be recog- 

 nized by the difference in form of the superior condyles of the 

 maxilhr, the variation of which will be discussed later. 



Now it seems to me that, if X. molossus and X. thaumas are 

 distinct species, Professor Cope failed to designate any constant 

 characters by which they can be determined, and, until it is 

 shown that such characters exist, we can do nothing more than 

 call them synonymous. I have carefully compared the descrip- 

 tion and figure of Doctor Leidy's specimen with specimens of 

 fin-spines in our collection that undoubtedly belong to one of 

 these species, and find them identical with the description. 

 This being the case, we must, for the present at least, consider 

 A', molossus and X. titan. mas Cope as synonyms of Xiphactinus 

 audax Leidy. 



Xiphactinus audax. Plates XXXIII to XLVII. 



Sfiurocrplialu* thaumas Cope. Proc. Am. Phil. Soc. 1870, p. 533. 

 Saurocephalus audax Cope, Proc. Am. Phil. Soc. 1870, p. 533. 

 Portheus molossus Cope, Proc. Am. Phil. Soc. 1871, p. 17-1: Cret. Vert. 



West., pp. 194-19G. 

 Portheus than mas Cope, Cret. Vert. West., pp. 19G-201. 

 Xiphactinus audax Leidy, Proc. Acad. Nat. Sci. Phil. 1870, p. 12; Rep. 



U. S. Geol. Surv. Terr. 1873, p. 290, pi. xvn. 



This species is by far the best represented of the physostomous 

 fishes in the University collection, the material consisting of 

 several individuals, some of which are almost complete and 

 others remarkably well preserved in certain parts, so that from 

 this material a better idea of the anatomy can be gained than 

 from any of the other collections that have been described. 



26. 1. c, p. 27. 



