NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 21 



Meniscotherium chamense Cope, 1874 

 Synonyms. — Meniscotherium terraerubrae Cope, 1881 ; Hyracops 



socialis Marsh, 1892 

 Type.— Right maxilla, U.S.N.M. 1093, with M^M* and part of P 4 . 

 Horizon and locality. — San Jose formation, San Juan Basin, N. Mex. 

 Range. — Largo facies, San Juan Basin, N. Mex. ; mid-Wasatchian, 



Piceance Creek Basin, Colo. ; Lost Cabin, Wind River Basin, Wyo. ; 



and New Fork, Green River Basin, Wyo. Middle and late Wasatchian 



early Eocene. 

 Meniscotherium tapiacitis Cope, 1882 



Type. — Portions of both rami of mandible, A.M. 4425, with P 3 -M 3 



represented. 

 Horizon and locality. — San Jose formation, San Juan Basin, N. Mex. 

 Range. — San Juan Basin, N. Mex. ; mid-Wasatchian, Piceance Creek 



Basin, Colo. ; early to mid-Wasatchian, Green River Basin, Wyo. 

 Meniscotherium priscum Granger, 1915 



Type. — Portion of left ramus of mandible, A.M. 16145, with Dp 4 and M v 

 Horizon and locality. — Clarkforkian late Paleocene, Clark Fork Basin, 



Wyo. 

 Range. — Not known outside occurrence of type. 

 Meniscotherium semicingulatum Russell, 1929 

 Type.— Right Dp 4 , Univ. Alberta, Dept. Geol. 120. 



Horizon and locality. — Late Paleocene (?), Cochrane, Alberta, Canada. 

 Range. — Not known outside occurrence of type. 

 Meniscotherium robustum Thorpe, 1934 

 Type.— Skull and lower jaw, Y.P.M. 10101. 

 Horizon and locality. — Knight beds near Aspen, Wyo. 

 Range. — Middle to late Wasatchian Knight beds beneath 



Fontenelle or Tipton tongue of Green River formation in south- 

 western Wyoming. 



Among the foregoing I suspect that only three species are valid. 

 These I regard as M. chamense, M. tapiacitis, and M. robustum. 

 Although there would appear to be certain characters other than size 

 of the skull and postcranial skeleton that may be significant in distin- 

 guishing between the two larger forms M. robustum and M. chamense, 

 size seems to be the only generally definable feature in their separation 

 and is consistently applicable in the Wyoming area. The much 

 smaller M. tapiacitis type has been characterized by the weakness of 

 the metastylids of the lower molars, but I find this is somewhat 

 variable in other materials, so that its better development in the 

 correspondingly small M. priscum type is probably unimportant. 

 The latter is tentatively retained only because of its earlier geologic 

 age. M. semicingulatum also may not be definable, since its descrip- 

 tion is evidently based essentially on a deciduous lower premolar. 

 Its size would not distinguish it from M. chamense, but its geographic 



