BUNOTHERIA. 805 



presence of the eubsquamosal foramen is on the other hand a marsupial 

 character. The absence of any but rudimental neural spines of the cervical 

 vertebrae is again an important difference from Bidelphys. 



The evidence is in favor of the Leptictidce, as represented by 3Iesodectes, 

 being a group of Biinotheria, and a member of the Creodonta, as defined by 

 the form of the superior molar teeth. 



Mesodectes canicdlus Cope. 



Imcis canicidiis. Paleontological Bulletin No. 16, p. 3. Anu. Report U. S. Geol. Survey Terrs., 1373 



(1874), p. 473. 



Plate LXII; figs. 33-50. 



This species is represented by portions of the skeletons of six individ- 

 uals. All of these lack the anterior teeth of both jaws, while one includes 

 mandibular teeth with vertebrae, ribs, humerus, scapula, presternum, a large 

 part of the cranium, &c. 



The basioccipital and sphenoid have straight lateral borders which 

 are slightly decurved into a low ridge on each side. A low median ridge 

 includes with these two a pair of longitudinal shallow fossae, which fade 

 out on the sphenoid bone. The occipital condyles are divergent, and with 

 very small laterally -looking portion. The foramen magnum is largely trans- 

 verse. The exoccipital does not extend far forwards, and the mastoid has a 

 very short anteroposterior extent. A foramen issues from the base of the 

 fossa inclosed by the longitudinal crests of the posterior part of the squa- 

 mosal bone, and there are two other foramina above the superior of these 

 crests. A small foramen pierces the same bone behind the inner extremity 

 of the external half of the postglenoid jirocess A groove follows the free 

 posterior edge of the squamosal, separating it from the mastoid. The petrous 

 is somewhat rectangular in its sections, and its transverse diameter exceeds 

 its anteroposterior. The inferior face is horizontal in the outer half, and 

 looks forwards and inwards on its inner half. 



The first rib is little compressed, and becomes very robust towards and 

 at the distal extremity, where it is truncate for articulation with the praester- 

 num. The extremity is oval in section. 



The shaft of the humerus is somewhat curved, and the anterior com- 



