M. R. Thorpe — A New Merycoidodon. 33T 



upper half of the inner side bears a distinct articular facet 

 while the distal half of the bone is laterally compressed, 

 ending in a blunt point. There is no indication of any 

 phalanges accompanying this first metatarsal, if such it is, 

 and the evidence certainly bears out the belief that it is the 

 vestige of the hallux, present in the earliest forms of the 

 Merycoidodontidas, such as Protoreodon, but not pre- 

 viously noted as occurring in the Oligocene forms. 



Specimen No. 12754, Y. P. M., consists of a skull and 

 jaws from the upper nodular layer of the Middle Oligo- 

 cene of South Dakota. It resembles M. culbertsonii in 

 all essential respects, although it is considerably larger 

 than the type. In fact, it probably represents a form 

 intermediate, both structurally and stratigraphically, 

 between M. culbertsonii and Eporeodon major. The 

 bullae are small and the lacrymal fossae deep. 



Measurements (Cat. No. 12754, Y. P. M.). mm. 



Total length, partly estimated 217 



Postorbital constriction, diameter 29 



Brain-case, maximum diameter 55 



Superior molars, length " 52 



Superior premolars, length 46 



Inferior molars, length _ 54.5 



Inferior premolars, length 47.5 



Merycoidodon culbertsonii pericnlo rum (Cope) 1884. 



This Middle Oligocene subspecies is represented by over 

 fifty individuals in the collection, mainly from Colorado 

 but a few from Nebraska and Wyoming. It differs but 

 slightly from M. culbertsonii except in its smaller size. 

 The length of the superior molar-premolar series varies 

 from 72 to 77 mm. ; the molar, from 40 to 42 mm. ; and the 

 premolar series has a length of 33 mm. The inferior 

 molar-premolar length is 73 mm., with a molar length of 

 47 mm. The above measurements were derived from 

 a considerable number of specimens. Cat. No. 12605, 

 Y. P. M., has a bizygomatic diameter of 89 mm., a maxi- 

 mum brain-case diameter of 44 mm., and a postorbital 

 constriction diameter of 30 mm. 



The age classes, based on forty specimens, are as 

 follows : 0-3, 6 individuals, or 15 per cent ; 4-6, 26, or 65 

 per cent; 7-8, 6, or 15 per cent; and 8-10, 2, or 5 per cent. 



