1881,] ^•^'^ [Cope. 



Measurementg. M. 



_. ^, -r. TTT (anteroposterior 006 



Diameters of base P-m. Ill -{ ^ . _„ 



(transverse 007 



,, ex. -n T-tr (anteroposterior 008 



" of base P-m. IV -< ^ ^,^ 



( transverse 010 



„, - ,T TT (anteroposterior .011 



" of base of M. II ■< „,„ 



(transverse 013 



r vertical 005 



" inferior P-m. Ill (or IV) \ anteroposterior . . . .007 



(_ transverse 005 



Depth of ramus at same tooth. 012 



Thickness ramus at succeeding tooth 009 



The Meniscotherium terroBVubrcB differs from the M. chamense in two 

 features. The first is its superior size. The second is the flattened form 

 of the external faces of the true molars and the absence of the convexity 

 of the external bases of the crown. 



My specimen of this species is from the red Eocene bed in JSTorthwestern 

 New Mexico, from the true Wasatch horizon, or higher than that which 

 produced the other species here described. It was found by my assistant, 

 D. Baldwin. 



Remarks. 



As stated in my report to Lieut. Wheeler in 1877, no vertebrate remains 

 had been found in the Puerco beds, which underlie the Wasatch in Xew 

 Mexico, up to that time. It was therefore uncertain whether they form 

 the top of the Cretaceous or the bottom of the Tertiary series. I have 

 recently obtained evidence of the existence of Ghampsosaurus in them, so 

 that their position might be supposed to be in the Postcretaceous S3'stem. 



It is however quite possible that the species of Mammalia described in 

 this paper were derived from the Puerco Formation. Their horizon is be- 

 low the Wasatch, and they represent a different fauna from that of those 

 beds. 



Attention has already been directed to this fauna in the pages of the Amer- 

 ican Naturalist.^ I have recorded the presence of the Ci'eodont genera, 

 Periptychus, Tri'isodon and Deltatherium, and of the saurian CJiainp- 

 sosaurus. I have now added the genera Ryracotherium and Meniscotherium, 

 and a number of new forms of considerable interest. These are the Creo- 

 dont Mesonyx, a new genus allied to Estlionyx, and a series of genera and 

 species with a suilline type of dentition, but whose aflinities are by no 

 means certain. This point cannot be determined until the characters of the 

 feet are known. 



The facies of this fauna differs in several points from that of the 

 Wasatch. Coryplwclon has not yet been discovered in it, and the flesh- 

 eaters are very primitive. The suilloid genera are characteristic. 



* April, August and October, 1881. 



