8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



SYSTEMATIC DESCRIPTION OF THE MAMMALIA 



MARSUPIALIA? 

 DIDELPHIDAE? 



PERATHERIUM?, sp. 



The isolated lower molar, Amherst No, 10019, which A. E. Wood 

 (1949) regarded as questionably representing Metacodon does not 

 seem to me to be insectivore. His careful drawing of this tooth sug- 

 gests possibly a closer relationship to the marsupials. I am particularly 

 impressed by the lingual position of the hypoconulid, and the posterior 

 deflection of the crest on which this cusp is located, away from the 

 entoconid. The talonid appears to be quite different from the structure 

 seen in Ictops and is unlike that, for example, in M2 of Metacodon 

 mellingeri where the hypoconulid is closely connected to the entoconid. 

 For these reasons I have tentatively assigned this specimen to Pera- 

 theriumf, sp. 



LAGOMORPHA 

 LEPORIDAE 



MYTONOLAGUS WYOMINGENSIS Wood, 1949 



Plate I, figure i 



A. E. Wood (1949) has described several isolated teeth of 

 Mytonolagus from the Badwater area and a comparatively unworn 

 P^ was designated the type of Mytonolagus wyomingensis. A right 

 maxilla (U.S.N.M. No. 21090) with P^-]\P collected by F. L. Pearce 

 undoubtedly represents the same species. P^ in this specimen, however, 

 is more worn than in the type, although the teeth in general appear to 

 be less worn than in the type of Mytonolagus petersoni which Burke 

 (1934) described from Uinta C at Myton pocket. The teeth are strik- 

 ingly like those in the type of M. petersoni, but it is noted that the 

 hypostriae on M2 and particularly Mi are more persistent, extending 

 nearly to the upper limit of the enamel lingually. The comparative 

 weakness of the lingual fold toward the root of M^ in M. petersoni 

 was further noted in upper-tooth material of the Myton form in the 

 collections of the National Museum. At least the hypostria extends 

 nowhere near the upper limit of the enamel. Wood has regarded M. 

 wyomingensis as perhaps more primitive than M. petersoni. 



