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1884. ] The Condylarthra. 793 
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 
itis the most primitive type of the Ungulata. A number of gen- 
era and species belong to it, and these fall into three families, 
which are defined as below. They conform to the definitions of 
the order in possessing the full mammalian number of teeth, 
and a third trochanter of the femur. The approximation to 
the Hyracoidea is greater than that of any other group of 
the Ungulata. 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- 
tior face of the extremity of the fibula, seen in no other group of 
ungulates. In the manus of the Hyracoidea the lunar bone 
agrees with the Condylarthta in not being divided below into two 
facets, as in most other ungulates, but it is peculiar in extending 
to the trapezoides (the intercalare), and to the unciform. In this 
Point the Hyracoidea come nearer to the Amblypoda. In Hyrax 
there is also no epicondylar foramen. The three families of Con- 
dylarthra are defined as follows: 
Dentition bunodont; toes 5-5; astragalus without trochlea ; neck very short; pre- 
molars very simple above and below Periptychida 
Dentition bunodont; toes 5-5 ; astragalus with trochlea; neck longer; premolar 
teeth different from the molars above and below . . Ph lontid 
Dentition lophodont, with crescents and deep valleys; premolars partly like molars 
` below; neck longer ? Meniscotheriid 
The bunodont dentition, with very simple premolars, flat astrag- 
alus and five toes on all the feet, give the Periptychidæ the lowest 
Place in the sub-order and order, as the most generalized type 
wn. The Meniscotheriidæ have a quite specialized dentition, 
and until I learned its Condylarthrous character, I was at a loss 
to account for the presence of such perfection in so old a type. 
number of the toes is yet unknown. The family appears to 
have had no descendants, and is a good illustration of Dr. Kow- 
alevsky’s views as to the persistence of the “ adaptive ” over the 
non-adaptive ” types of articulation. Kowalevsky observed that 
the types of Ungulata, which have the carpo-metacarpal and 
tarso-metatarsal articulations simple and not alternating, have 
Ome extinct. In those which persisted, the metapodials artic- 
with two bones of the carpal or tarsal series. Ihave dis- 
E ed that the same rule has generally applied in the ungulates 
