102 Bulletin American Museum of Natural History. [Vol, X, 



and the longitudinal grooves u])on the superior intranareal sur- 

 faces of the maxillaries (also observed in Coryphodoii). The 

 proportions and characters of the skull (exclusive of the teeth) 

 are identical with those in the ancient Amblypoda, such as Perip- 

 tychus and Paniolambda. 



The distinctive feature of the vertebral column is the small 

 number of dorsal vertebrae, namely 15, exactly as in Coryp/iodoii 

 and Tttaiioiheriiii/i, ^wmo^ a dorso-lumbar formula of 20-21. In 



i^:^5:n>^. 



Fig. 3. Skeleton of Pkenacodus pritnieTUs placed in the standing position to show elevation 

 of the withers. One-twelfth natural size. 



the writer's opinion this number is characteristic of tlie primitive 

 Condylarthra or Protungulata. Marsh,' on the other hand, has 

 assigned to the Holodactyla (Condylarthra) 23 dorso-lumbars, 

 and to the Protungulata 30 dorso-lumbars or more. The second 

 distinctive feature is found in the splitting of the transverse pro- 

 cesses on the posterior dorsals for articulation with the tubercles 

 of the ribs and for the support of the zygapophyses respectively, 

 as shown in Fig. 2, these processes being sharply separate. 



' ' Dinocerata,' pp. 171, 172. 



I 



