148 Bulletin American Miiseitm of Natia-al History. [Vol. XII. 



may be that the specimen represents only a smaller variety of P. 

 osstfraga and is not entitled to a specific rank, but in view of the 

 fact that it furnishes just the character which, upon general 

 grounds, one would be led to anticipate, I have thought fit to 

 give it the above name. 



This virtually completes the series of the Dissacus-Pachyana 

 Mesonyx phylum and establishes a closely connected specific 

 descent reaching in time from the Torrejon to the White River 

 without any important break. The Wind River representative of 

 this series, however, yet remains to be discovered, but in accord- 

 ance with what we already know its characters can be most 

 accurately predicted. 



EXPLANATION OF PLATE VIL 



OxycEiia lupitia. Cope. Skeleton, ^th natural size. No. 107, Am. Mus. Coll. 

 The specimen described and figured as "No. 2" by Prof. Cope in 'Ter- 

 tiary Vertebrata of the West,' (p. 319, pi. xxiv^, tigs. 12-15, and pi. xxiw/, 

 figs. I-18) is a part of this individual. 



