788 THE WHITE EIVER FAUNA. 



MARSUPIALIA. 



Cuvier demonstrated the existence of species of this order in the 

 gypsum of the upper Eocene of Paris, and additional species have been 

 made known by Aymard, Filhol, and others. In 1873 I discovered in 

 Colorado a number of species which agree very closely with the French 

 forms, so far as can be ascertained from the dentition. These I referred to 

 the Insectivora,^ but subsequently identified^ them as Marsupialia. They 

 are nearly related to the European forms, and whether they can be placed 

 in a distinct genus remains to be ascertained. A species of the same group, 

 if not the same genus, is described in Part I of this volume, from the Wind 

 Eiver Eocene (page 269). 



Along with these species were found several others, less evidently 

 members of the Marsupial order. I refer to the genera Mesodectes, Domnina, 

 and Menotherium. Close allies of the first of these had already been refen-ed 

 by Leidy to the Insedivora. I have in the first part of this book placed 

 the group in the suborder Creodonfa and the family of Lcptididce, but with a 

 feeling of uncertainty whether the family may be Marsupial or not. Dom- 

 nina is, I suspect, chiropterous Menotherium resembles the Leptictidce, but 

 still more the Ifesodonta, where I originally placed it. I leave it there for 

 the present in the immediate neighborhood of the genus ApheUscus. For 

 purposes of determination from dental characters I compare these genera 

 in a table, as follows. Some of them have been already defined in the ana- 

 lytical table of the genera of Creodonta, page 269. 



I. Fourth inferior premolar constructed on the type of the true molars, with three an- 



terior cusps. 

 Mental foramen anterior, below fourth premolar; inferior true molars subequal. 



Peratherium. 

 Mental foramen below first true molar; inferior molars diminishing in size posteriorly, 



Domni7ia. 



II. Fourth i^remolar with three anterior cusps, as in I; but unlike true molars; 

 True inferior molars with only two cusps in front Mesodectes. 



III. Fourth premolar simple; unlike true molars; 



True inferior molars with two anterior tubercles Menotherium. 



'Anuual Report U. S. Geol. Surv. Terrs., 1873 (74), p. 465. 

 »3ulletiu U. S. Geol. Surv. Terrs., 1879, p. 45. 



