514 Reviews — Prof. Edward I). Cope — 



Didelphis in the elevation of the median cusps of the superior true 

 molars into Vs, and in the tubercles of the external series becoming 

 obsolete. All the species are founded on dental characters. 

 Mesodectes and Geolabis are referred provisionally to the Creodonta. 

 The former is intermediate between Leptictis and Ictops, the last 

 premolar having a single sharp cusp as in the former genus, with an 

 internal cusp or heel like that of the latter. The cranial characters 

 are like those of Leptictis, and the molars and some other features 

 recall the living genus Solenodon. The presternum has a prominent 

 keel in front, like that of a bird. The cerebral hemispheres and 

 cerebellum are a little wider than long, and together have a sub- 

 quadrate outline. The only species known is about the size of the 

 Hedgehog. Geolabis is only known from crania, from which the 

 molar teeth are wanting, and the author is uncertain whether it may not 

 be identical with Domnina. Menotherium lemurinum, though placed 

 under the Insectivora, is regarded as the first indication of a Lemur 

 in the Miocene of the United States, and indicates an animal as large 

 as the domestic Cat. The genus Domnina is referred with some 

 doubt to the Cheiroptera. It has the posterior external cusp of the 

 true molar teeth in the form of a crescent, like the anterior cusp, 

 only rather smaller ; both internal cusps are at the summits of strong 

 ridges : two species are described. 



The order Eodentia is represented by no fewer than thirty-one 

 species and eight genera, of which Sciurus, Hesperomijs and Lepus 

 are found living in the same region, and all the fossil species of Kodents 

 belong to the three great divisions of the order which now inhabit 

 North America. The author observes that the feet and teeth in this 

 order present a succession of changes in structure with time. The 

 earliest known forms, allies of the Squirrels, belong to the sub- 

 order Sciuromorpha. In them the trochlear structures of the hume- 

 rus and tibia are but little developed, they are plantigrade, with five 

 digits, and the fibula is not co-ossified with the tibia, while their 

 teeth have nearly always long roots and short crowns, and are rarely 

 prismatic. An advance on this generalized type is seen in the sub- 

 order Histricomorpha (which has a single representative in the 

 Loup Fork beds), in many of its members having a reduced 

 number of digits and prismatic dentition. In the third suborder, 

 Myomorpha, the tibia is found co-ossified with the fibula ; many 

 genera have prismatic teeth, some a reduced number of digits, and 

 a few, comprising the Jerboas, have the metatarsal bones blended 

 together. Finally, the Eabbits add to these specialized characters 

 a primitive character in the presence of four superior incisor teeth ; 

 and the author is disposed to believe that the Eodents are either 

 direct descendants from the Marsupials, or that the Eabbits may 

 represent the suborder Tillodonta of the Eocene. The differentiation 

 of the Eodent suborders, however, must be anterior to the Miocene 

 period, for the Squirrel tribe has already occurred in the Lower 

 Eocene. The Myomorpha appear in the John Day beds, but without 

 prismatic teeth, while the Lagomorpha are typically developed in the 

 White Eiver beds, and a true Porcupine represents the Hystrico- 



