VERTEBRATA : MAMMALIA. 725 



ally so diminutive that it could apparently have been drawn 

 through the neural canal of all the prsesacral vertebrae, cer- 

 tainly through the cervicals and lumbars." 



The chief genera which are included amongst the Dinocerata 

 by Marsh are Dinoceras, Tinoceras, and Uintatherium. All 

 the remains of this singular group which have hitherto been 

 brought to light, are from the Eocene rocks of North America. 



ORDER VIII. TILLODONTIA. This order has been estab- 

 lished by Prof. Marsh for the reception of some singular Mam- 

 mals from the Eocene Tertiary of the United States. The 

 following are the characters of the order, so far as published : 

 The molar teeth have grinding crowns, as in Ungulates, and may 

 have distinct roots, or may grow from permanent pulps ; small 

 canines are present in both jaws ; and each jaw carries two long 

 scalpriform incisors, resembling those of Rodents in form and in 

 growing from persistent pulps. The feet are plantigrade and 

 pentadactyle, and the digits were apparently unguiculate. The 

 femur has a third trochanter, and the radius and ulna and tibia 

 and Jibula are distinct bones. 



The order includes two distinct families, one, the Tillothe- 

 rid&, having molar teeth with distinct roots ; whilst the other, 

 Stylinodontidce, possessed rootless molars, which grew from 

 persistent pulps. All the known forms of the order are from 

 the Eocene Tertiary, and the typical species seem to have 

 been from one-half to two-thirds of the size of the Tapir. 



The type-genus of the order is Tillotherium, which presents 

 a remarkable combination of the characters of the Ungulata, 

 Rodentia, and Carnivora. The general form of the skeleton 

 most closely resembles that of the Carnivores, the skull being 

 like that of the Bears in many respects, whilst the feet are five- 

 toed, with the whole sole applied to the ground, and having 

 ungual phalanges similar to those of the Ursidce. The brain- 

 cavity is of small size, and the cerebral hemispheres did not 

 extend over the cerebellum or the olfactory lobes. The orbits 

 are not complete, but open into the temporal fossae. The 

 prsemolars and molars have grinding crowns, the canines are of 

 small size, and the praemaxillae carried a pair of large scalpri- 

 form incisors (fig. 414), which resemble those of the Rodents 

 in having chisel-shaped crowns, and in growing throughout 

 the life of the animal. As in Rodents, there is a correspond- 

 ing pair of scalpriform incisors in the lower jaw. The dental 

 formula is 



. i i i T i * * 3 



i - - ', c - ; pm - - ; m -- = 30. 



!_!> !_!> * 2 _ 2 ' 33 



