CONDYLAETHEA. 385 



throus character, I was at a loss to account for the presence of such per- 

 fection in so old a type. The number of the toes is yet unknown. The 

 family appears to have had no descendents, and is a good illustration of 

 Dr. Kowalevsky'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 articu- 

 lations simple and not alternating, have become extinct. In those which 

 persisted, the metapodials articulate with two bones of the carpal or tarsal 

 series. The same rule has generally applied in the Ungulates to the distal 

 astragalar articulation. The orders with the double articulation have left 

 descendents, while the Condylarihra with the single articulation have disap- 

 peared without leaving a trace. The Proboscidea, which have the same 

 simple distal articulation, still remain, however, to show an exception to the 

 generalization. They have, however, an alternation in the second series 

 of the posterior foot not present in the Taxeopoda. The relations of the 

 genera of these three families are as follows : 



Periptychidae. 

 In Periptychus only are the posterior feet known. The carpus is yet 

 unknown. The successional modifications are seen in the addition of cusps 

 to the inner sides of the premolars of both jaws, and the true molars of the 

 upper jaws. In Periptychus we have the largest number of dental cusps 

 and lobes, and in Anisonchus the next. With that genus the inferior pre- 

 molars lose their inner ledges, and the true molars their anterior internal 

 lobes. The latter are still further reduced in Hemithlceus, and the former in 

 Haploconus. It is possible that Conoryctes belongs to this family. In all of 

 my specimens of this genus the faces of the molars are so worn that I can- 

 not see the pattern, and the ungues are unknown. There is, however, a 

 general agreement in the known parts of the skull and skeleton. If it enters 

 here it will be characterized by the perfect V's of the inferior molars. The 

 following are the characters of the genera: 



I. Intermediate tubercles present; inferior premolars with internal lobes. 

 Superior molars with two internal cusps besides apex of V; superior premolars with 



internal lobes Periptychus. 



25 o 



