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



low and broad ; lower jaws with condyle facing upwards and 

 backwards; prominent depression posteriorly; a mental foramen 

 below first premolar, a second mental foramen below lower 

 canine. 



Dentition.— "Wi^ superior teeth, wanting in this specimen, are 

 perfectly preserved in No. 2829, and agree with the fragmentary 

 type specimen of Coryphodon (B.) radians Cope. 



Vertebral formula : C.7, D.15, L.5, S.4. 



This remarkably low vertebral formula is ascertained from 

 No. 2829, in which all the dorsals and lumbars are retained in a 

 single block and can be counted with considerable certainty. 

 The formula is very low, but not more so than in Titanoi/icriiim, 

 in which D. L. = 20. The chief characteristic of the vertebral 

 column is the series of low, undifferentiated neural spines, which 

 are ill correlated with the heavy skull. 



Ceivicals. — Atlas moderately broad with a slightly expanded 

 transverse process, perforated slightly above the base by the ver- 

 tebrarterial canal. The spine of the axis extends equally forwards 

 and backwards. The remaining cervicals exhibit a gradual 

 development of the inferior lamella, which is well marked in C.6, 

 but lacks the strength exhibited in the larger Perissodactyla. 

 The cervical centra are very short, and the vertebral centra grad- 

 ually increase in length and depth toward the lumbar region. 



The most striking feature of the dorsal vertebrae, which is 

 shared by Plienacodns, is the great prominence of the transverse 

 process supporting the tubercle of the ribs. This projects widely 

 out from the side of the vertebra in D.i, and gradually recedes to 

 D.ii, which is apparently the last vertebra in which the rib tuber- 

 cle articulates. In all the dorsals the head is placed directly be- 

 tween the adjacent vertel)rae from D.i to D.15. The low spines 

 characteristic of the cervical region extend back as a feature of 

 the dorsals, the vertebrae exhibiting terminal tuberosities for the 

 fascia of the ligamentum nuchse. The dorsal vertebral spines 

 gradually thicken in antero-posterior diameter ; as they pass 

 backwards they decrease in height. In the lumbar region they 

 are cleft on the dorsal line. The lumbars terminate inferiorly in 

 compressed keels. 



