FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



267 



The classification seems, in fact, to have been based on grades of foot 

 specialization, over the prototypal ungulate foot, rather than on 

 characters peculiar to natural phyla. It thus united periptychids 

 and pantolambdids because they had advanced relatively little in 

 limb structure, even though their phyletic relations must have been 

 distant. It separated (subordinally) pantolambdids and cory- 

 phodonts because the former were less and the latter more advanced in 

 limb specilization, despite the clear evidence that these groups are 

 closely related phyletically. And finally it united coryphodonts and 

 uintatheres because both have specialized limb structures, but over- 

 looked their marked phyletic separation. 



The revision of nomenclature for the accurate representation of 

 these newer points of view is difficult. The following diagram shows 

 the relationships of the classic names to the groupings now considered 

 natural : 



Since both periptychines C'Catathlaeus") and anisonchines {Anison- 

 chus) were explicitly cited among the genera belonging to the Con- 

 dylarthra when that group was first proposed, since most definitions 

 of Condylarthra need little or no alteration to include the periptychids, 

 and since no other ordinal or subordinal name has been based primarily 

 on the periptychids, the removal of the Periptychidae to the Condy- 

 larthra raises no nomenclatural problem. 



