732 THE EOCENE FAUNA. 



Measurements of a vertebra. 



M. 



Length of centrum (with ball) 0070 



rv- » r 1 11 < vertical 0035 



Diameters of ball < „„,„ 



( transverse wifj 



Elevation of vertebra at epispheu 0085 



Elevation of vertebra at middle 0062 



Width at prezygapophyses 0120 



Width of tubercular costal faces - 0105 



Width of zygantrum 0058 



Vertical diameter costal faces 0040 



Transverse diameter tubercular costal face 0028 



This snake was about the size of the black snake, Bascanium constrictor. 

 It is an interesting species for two reasons. First, it is the oldest sequent 

 known from North America. Second, in the imperfection of the zygantrum 

 we observe<an approximation to the ordinary reptilian type of vertebra, from 

 which the ophidian type was no doubt derived. In the former there is no 

 zygosphen or zygantrum. 



MAMMALIA. 



POLYMASTODON Cope. 



American Naturalist, August, 1882, (July), 684. 



Known only from the inferior dentition. Supposed formula : I. 1 ; C. 

 0.; Pm. 0; M. 2. The first true molar is large, exceeding the second, and 

 supports three longitudinal series of tubercles. Function of the molars 

 masticatory. 



In this genus the molar part of the dentition assumes the exclusive 

 control of mastication, having already displayed a predominance in Catop- 

 salis. The molars are similar in their general character to those of Piilodus 

 and C'atopsalis, but the three rows of tubercles distinguish them from both. 



But one species is yet known. 



POLYMASTODON TAOENSIS Cope. 



American Naturalist, August, 1882, (July), 684. 

 Plate XXIII c; fig. 6. 



Portions of both mandibular rami of this species with the molar teeth 

 are the only parts of this singular animal yet known to me. The inferior 

 borders and angles of the rami are lost. 



