MAMMALIA. SUBUNGULATA. 361 



Suborder (1). TOXODONTIA. 



This suborder includes some very aberrant extinct South 

 American ungulates, which have characters recalling the 

 Proboscidea, both groups of Ungulata vera, and the Rodentia. 

 The limbs are subplantigrade or digitigrade, and the digits 

 are three, rarely five, in number, the third being most 

 developed. The carpus resembles that of the Ungulata vera, 

 in that the bones interlock and the magnum articulates with 

 the scaphoid. In the tarsus, however, the bones do not 

 interlock. The astragalus has a pulley-like proximal sur- 

 face (except in Astrapotherium, in which it is flat), and 

 articulates only with the navicular, not meeting the cuboid. 

 The calcaneum has a large facet for articulation with the 

 fibula, as in Artiodactyla. There is no alisphenoid canal, and 

 the orbit is confluent with the temporal fossa. Some of the 

 forms (e.g. Nesodon) referred to this group have the typical 

 mammalian series of forty-four teeth, but in others the canines 

 are undeveloped. In Toxodon all the cheek-teeth have persist- 

 ent pulps, while in Nesodon and Astrapotherium they are rooted. 

 A clavicle is sometimes present (Typotherium), and the femur 

 sometimes has a third trochanter (Typotherium and Astra- 

 potherium), sometimes is without one (Toxodon). 



The remains of these curious Ungulates have been found 

 in beds of late Tertiary age in South America. 



Suborder (2). CONDYLARTHRA 1 . 



This group includes some comparatively small extinct 

 ungulates, which are best known from the Lower Eocene of 

 Wyoming, though their remains have also been found in 

 deposits of similar age in France and Switzerland. Their 



1 See E. D. Cope, "The Condylarthra," Amer. Natural., 1884, and 

 "Synopsis of the Vertebrates of the Puerco series," Tr. Amer. Phil. Soc., 

 1888. 0. C. Marsh, "A new order of extinct Eocene Mammals (Meso- 

 dactyla)," Amer. J. Sci., 1892. 



