Wortman — Studies of Eocene Mammalia, etc. 377 



Art. XLT. — Studies of Eocene Mammalia in the Marsh 

 Collection, Peabody Museum ; by J. L. Wortman. 



[Continued from p. 296.J 



The Vertebral. — With the exception of the right half of the 

 atlas, and perhaps more than half of the caudals, the vertebral 

 column is present in its entirety ; it is preserved, moreover, 

 very nearly in its natural position, with the vertebrae inter- 

 locked in such a manner that there can be no doubt whatever 

 of the presacral formula. 



The atlas bears a very strong resemblance to that of the 

 felines. The transverse process is proportionally less extended 

 and does not project so far behind the facets for the axis ; it is 

 emarginate behind, considerably thickened, and pierced by the 

 canal for the vertebral artery much as in the cats. The ante- 

 rior margin of the process displays a deep notch, in which the 

 artery winds forward in its course to the sinus atlantis. This 

 latter has much the same relative size, position, and relation as 

 in the felines. The cup-shaped articular facets for the con- 

 dyles are large and roomy, the tubercle for the transverse 

 ligament prominent, and the superior arch is of good breadth. 



As Scott has remarked of Mesonyx, the axis exhibits some 

 peculiarities, the most conspicuous of which is the very large 

 backwardly projecting spine. The odontoid is rather long and 

 conical, the atlantal facets are large and slightly convex, the 

 body is strongly keeled, and the transverse process long and 

 tapering. The spine rises high above the body ; it projects 

 comparatively little forward, reaching only opposite to the root 

 of the odontoid, but posteriorly it is produced into a long 

 tapering process, which overhangs nearly the entire third cer- 

 vical. The remaining cervicals, like the atlas and axis, are 

 proportionally stout and heavy, evidently in relation with the 

 large size of the head. Their neural spines increase rapidly in 

 height, that of the last almost equaling in length that of 

 the first dorsal. The bodies of all the anterior cervicals have 

 strong inferior keels which bifurcate posteriorly and terminate 

 in two long protuberances. The plan of arrangement of the 

 transverse processes is similar to that of the Carnassidents. 

 The costal processes or inferior lam ell 83 are small in the ante- 

 rior vertebrae, but increase rapidly in size to the seventh. The 

 vertebra prominens has a simple transverse process, which is 

 not perforated by the vertebrarterial canal. 



The dorso-lumbar formula is 19, as in the Marsupials, 

 whereas it is very generally 20 among the Carnassidents. There 

 is reason to believe that all the Creodonts had the marsupial 



