I328 CLASS MAMMALIA. 



fourth upper premolar has two outer columns in place of the single 

 one of the typical section (fig. 1201). Coloreodon differs from 

 Agriochozrus by having only three premolars, but it may be ques- 

 tioned whether this difference really affords sufficient grounds for 

 generic distinction. The majority of the genera are confined to 

 the White River Miocene of North America, but Merycochcerus 

 extends into the Loup-Fork beds, which may be either of Upper 

 Miocene or Lower Pliocene age. A tooth, apparently indistinguish- 

 able from the molars of Agriochcerus, has been obtained from the 

 Pliocene of India. 



Here may be noticed a remarkable form from the Upper Eocene 

 of the United States, described under the name of Protoreodon. 

 The organisation is said to be of the Cotylopine type, but the 

 upper molars have five columns, as in the Anthracotheriidce and 

 Anoplotheriidce. This genus probably indicates an ancestral type of 

 the Cotylopidce, which should perhaps be referred to a distinct family; 

 it is, however, placed by Professor Cope near the Xiphodonts. 



Family Anoplotheriidce. — In this family the cheek-teeth are 

 imperfectly selenodont ; the crowns of the upper true molars (fig. 

 1204) carrying five columns, three of which are placed on the 

 anterior, and two on the posterior lobe, or half, of the crown. All 

 the bones of the limbs and feet remain distinct from one another ; 

 and there is no descending flange at the angle of the mandible. 

 The functional digits may be either two or three in number ; and 

 the carpus and tarsus of the original genus are of that type to which 

 the name inadaptive has been applied. 1 The anterior premolars 

 are more or less perfectly secant ; there is generally no diastema in 

 the dental series ; and the canines are short and compressed, and 

 depart very widely from those of the Anthracotheriidce. and their 

 allies, in which they resemble the corresponding teeth of the 

 Carnivora. In the type genus Anoplotherium (in which may be 

 included Eurytherium and Diplobune) the dentition (fig. 1204) is 



usually/ -, C. -, Pm. -, M. -; but occasionally the first lower 



3 I 4 3 



premolar is wanting. The tail (fig. 1203) is long; the functional 

 digits may be either three or two ; 2 and the third upper premolar has 

 a well-developed inner tubercle. In the typical A. commune, of the 



1 In the inadaptive modification {Anoplotherium) the carpals of the aborted 

 digits remain as useless lateral bones ; while in the adaptive modification 

 {Hyotherium) they shift their position, and take a share in the support of the 

 large persistent digits. 



2 Prof. Cope has suggested that the forms with two digits should be excluded 

 from this family, but it is the type species which presents this feature. The form 

 with three functional digits is indistinguishable by dental characters from the 

 typical A. commune with only two. 



