16 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



Although the skeleton of AI. europxus appears from the foregoing formula to 

 include one less thoracic vertebra than those of M. bidens, as the last pair of ribs 

 present is as long as the preceding ones, an additional pair ])robably existed origi- 

 nally. The formula for europseus would then be: C. 7, Th. 10, L. 10, Ca. 20 = 47. 

 (Pl.'l3,fig. 1.) 



In the Atlantic City specimen all the epiphyses are free. The atlas and axis 

 are anchylosed together, the third cervical is united to the axis by the centrum, 

 and on the right side by the top of the neural arch; on the left side the arch is 

 imperfect and free. The fourth to the seventh cervicals, inclusive, are all free. 

 The arch is incomplete above in the fourth, fifth, and sixth, but complete in the 

 seventli. There is a short neural spine on both sixth and seventh cervicals. The 

 atlas has a broad, obliquely-truncated inferior lateral process, but no superior 

 process, while the axis has both inferior and superior processes. The inferior 

 process is twice as long as the supei-ior process, and both are directed backward. 

 They do not meet to form a ring. The third to the sixth cervicals, inclusive, 

 have inferior processes only, that on the third being long and thin (but developed 

 on the left side only). On the fourth and fifth cervicals the processes are short 

 and small; on the si.xth, long and broad, and directetl downward. The centrum 

 of the seventh cervical has a broad facet on the side, where tlie first rib is attached, 

 and an inferior lateral process thicker than that of the sixth cervical, but also 

 directed downward. 



It is doubtful whether the foregoing characters of the cervical vertebrfe are of 

 any systematic importance, as there is a very large amount of individual variation 

 among these animals in the development of the transverse processes and other 

 details of structure. J/, hidens, however, appears to have superior transverse 

 processes on most of the cervicals which sometimes unite with the inferior proc- 

 esses to form foramina. In the specimen of J/, europseus under consideration there 

 are no superior processes, except on the axis. 



Metapophyses are first distinguishable on the diapophyses of the fourth thoracic 

 vertebra, and on the seventh assume the form of conical tidjercles. On the eighth 

 and following vertebrte they are flat, and are last tlistinguishable on the seventh 

 caudal vertebra. Facets for the articulation of the tubercles of the ril)s occur on 

 the diapophyses of the first to the seventh thoracic vertebrae. On the latter vertebra 

 the first transverse process appears as a siiort j)rojection on the side of the centrum. 

 On the eighth thoracic vertebra, the transverse ])rocess is broad and flat, with the 

 anterior margin bent upward, and is about 4S ram. long. The base of the neural 

 arch is strongly concave externally. The transverse process of the ninth thoracic 

 vertebra is similar to the preceding one, but broader and not bent upward anteriorly. 

 The base of the neural arch is also concave in this vertebra. The ends of the trans- 

 verse processes of the eighth and ninth vertebra? are emarginate for the articulation 

 of the ribs. A median inferior ridge is first distinguishable on the seventh thoracic 

 vertebra. 



As far as can be learned from the descriptions of Turner, Grieg, and others, 

 the thoracic vertebrae of europseus do not present any marked differences from those 

 of hidens. 



