Cope.] ^b [May 19; 



Amblypoda on the one hand, and the Perissodactyla and Ariiodactyla on 

 the other. Such will however probably be discovered. But the earliest 

 Perissodactyla, as for instance Hyracotherium, Hyrachyus and Triplopus, 

 possess the carpus of the later forms, Rhinocerus and Tapir us. The order 

 Amblypoda occupies an interesting position between the two groups, for 

 while' it has the carpus of the primitive type, it has the tarsus of the later 

 orders. The bones of the tarsus alternate, thus showing a decided advance 

 on the Taxeopoda. This order is then less primitive than the latter, 

 although in the form of its astragalus it no doubt retains some primitive 

 peculiarities which none of the known Taxeopoda possess. I refer to the 

 absence of trochlea, a character which will yet be discovered in the Taxeo- 

 poda, I have no doubt. 



The Taxeopoda approach remarkably near the Bunoth&ria, and the 

 unguiculate and ungulate orders are brought into the closest approxima- 

 tion in these representatives. In fact I know of nothing to distinguish the 

 Oondylarthra from the Mesodonta, but the ungulate and unguiculate 

 characters of the two divisions. In the Cveodontoj this distinction is reduced 

 to very small proportions, since the claws of Mesonyx are almost hoofs. 

 Some of the genera of the Periptychidce present resemblances to the 

 Greodonta in their dentition also. 



The facts already adduced throw much light on the genealogy of the 

 Ungulate Mammalia. The entire series has not yet been discovered, but 

 we can with great probability supply the missing links. In 1874 I pointed* 

 out the existence of a yet undiscovered type of Ungulata, which was an - 

 cestral to the Amblypoda, Proboscidea , Perissodactyla and Ariiodactyla., in- 

 dicating it by a star only in a genealogical table. This form was discov- 

 ered in 1881, seven years later, in the Oondylarthra. It was not uhtillaterj 

 that I assumed that the Diplarthra are descendants of the Amblypoda. 

 although not of either of the known orders, but of a theoretical division 

 with bunodont teeth.:): That such a group has existed is. rendered ex- 

 tremely probable in view of the existence of the bunodont Proboscidea and 

 Gondylartlira, That the Taxeopoda was the ancestor of this hypothetical 

 group as well as of the Proboscidea, is extremely probable. But here 

 again neither of the sub-orders of this group represent exactly the ances- 

 tors of the known Amblypoda, which have an especially primitive form 

 of the astragalus not found in the former. In the absence of an ankle- 

 joint, the Amblypoda are more primitive than any other division of the 

 Ungulata, and their ancestors are not likely to have been more specialized 

 than they. It is probable that a third sub-order of Taxeopoda has existed 

 which had no trochlea of the astragalus, which I call provisionally by the 

 name of Platyarthra. 



* Homologies and Origin of Teeth, etc., Journal Academy Xat. Science, 

 Philada., 1874, p. 20. 



t Report IT. S. Geoli Survey W. of 100th Mer., p. 282, 1877. 



J This hypothetical sub-order is called in the appended scheme, Amblypoda 

 Hyodonta. 



