i9°5-] 



MATTHEW— THE OSTEOLOGY OF SINOPA. 71 



marsupials in two or three other important characters, and differing 

 rather widely from the remaining creodonta. The lumbar region is 

 long and the vertebrae large with long transverse processes, indi- 

 cating a flexible body with great leaping powers, as in primitive 

 mammals generally. Among modern carnivora the cats, viverrines 

 and mustelines retain more of this character than the other groups. 



The limbs show a considerable degree of cursorial adaptation for 

 an Eocene carnivore, the bones being longer and the feet more 

 compact than in the majority of creodonts. The scapula is nearly 

 as long and narrow as in the dogs (the anterior border is incom- 

 plete and is restored too wide in the mount) ; the humerus com- 

 pares with that of the cat ; the femur retains a vestigial third 

 trochanter, but its distal end is deep and narrow, almost ungulate 

 in type ; the ulna is somewhat more robust than the radius, as in 

 creodonts generally, and in most insectivora and marsupials ; in 

 modern carnivora the shaft of the ulna is reduced to a varying 

 degree. 



There are five well developed toes on each foot and the axis of 

 symmetry in both fore and hind foot passes through the middle 

 digit (mesaxonic) as in Hyanodon. In all modern carnivora and 

 in the Mesonychidas among creodonts, the axis of symmetry lies 

 between the third and fourth digit (paraxonic). In the Oxyaenidas 

 the weight is distributed over comparatively short spreading digits 

 so that the axis of symmetry is not well defined (amphaxonic). 

 The scaphoid, lunar and centrale bones of the wrist are separate as 

 in creodonta, instead of united as in true carnivora ; the arrange- 

 ment of the carpals resembles that in Hycznodon, but their vertical 

 diameters are greater. The fibula is large and has a considerable 

 facet for the calcaneum, and the contact between astragalus and 

 cuboid is slight as in Hymnodon. 



The skeleton represents an undescribed species nearly allied to 

 S. rapax Leidy. The skull described by Wortman as Sinopa agilis 

 differs considerably in dentition, etc., and should be distinguished 

 generically ; the generic name Prototomus Cope, is probably avail- 

 able for this form. The most important distinctions from Sinopa 

 in the teeth are the closely connate paracone and metacone on 

 M 1 ---!, absence of metacone on M&, reduced heels of the lower 

 molars, and much compressed premolars. 



In all respects Sinopa appears as a primitive member of the 



