384 THE EOCENE PEKIOD. 



foramen, which is elsewhere unknown among ungulates. The humeral 

 condyles have the generalized character of the same type of the Amhlypoda, 

 and of the lower Perissodacti/la, in lacking an intertrochlear crest.' The 

 Condylarthra may then be further defined as follows r Astragalus with one 

 uniformly convex distal articular face ; humerus with epicondylar foramen. 

 This sub-order has as yet been only found in the lowest horizons of the 

 Eocene period, the Puerco and Wasatch, and only on the North American 

 Continent. Appropriately to this position in time, its structure indicates 

 that it is the most primitive type of the Ungulata. A number of genera 

 and species belong to it, and these fall into three families, which are detined 

 as below. They conform to the definitions of the order in possessing the 

 normal mammalian type of dentition, without specialization, and a third 

 trochanter of the femur. The approximation to the Hyracoidea is greater 

 than that of any other group of the Taxeopoda. That order agrees with 

 the Condylarthra in the simple articular extremity of the astragalus, which is, 

 however, less convex ; but it has a very peculiar articulation with the ante- 

 rior face of the extremity of the fibula, seen in no other group of ungulates. 

 In the manus of the Hyracoidea the lunar bone is very peculiar, not being 

 divided below into two facets, as in most other ungulates, and generally 

 extending to the carpals of the trapezoides series (the intercalare), as well 

 as to the unciform. In this point the Hyracoidea come nearer to the Atnbly- 

 poda. In Hyrax there is also no epicondylar foramen. The three families 

 of Condylarthra are defined as follows : 



Dentition buiKMloiit; toes 5 — 5; axtragaliis without trochlea; neck very short ; pre- 

 molars vf.Ty simple above and below Periptyvhida: 



Dentition bunodont; toes 5 — 5; astragalus with trochlea; neck longer; jiremolar 

 teeth different from the molars above and below . PheiuiaxhiHtiilw. 



Dentition loj>h(»dont, with crescents and deep valleys; premolars partly like molars 

 below; neck longer! Menigcotheriidcv 



The bunodont dentition, with very simple premolars, flat astragalus, 

 and five toes on all the feet, give the Periptychidce the lowest place in the 

 sub-order and order, as the most generalized type known. The Meniscothe- 

 riidce have a quite specialized dentition, and until I learned its Condylar- 



> American Naturalimt, Apnl, 168^, p. 334. 

 •Amer. NatnroliHt, 1881, p. 1017, Not. ». 



