274 



DOUGLASS FOSSIL MAMMALIA 



by a groove. The lower surface of the atlas is nearly flat with a median anterior con- 

 vexity, evidently terminated by a short spine or protuberance which has been broken off. 

 The posterior cotyles for the axis are nearly flat, and, like the anterior ones, are almost 

 confluent below. 



The odontoid of the axis is broad and (hick. As stated by Scott in the case of 

 Hyopolamus brachyrhyncus (1895, p. 470), it is " neither conical nor spout-shaped, but 

 intermediate between the two." It is broad and thick. A section at the base, also the 

 anterior edge, are almost semicircles, so the process is approximately the sector of a 

 sphere. The upper surface, however, is not flat, but somewhat irregular. Anteriorly it 

 is beginning to be spout-shaped, but there is a broad median convexity. Farther back 

 at the base is a greater prominence, terminating anteriorly in two V-shaped convexities, 

 one on each side of the median line. With the exception of this prominence and its 

 greater width, this process resembles that of Agriochosrus. The atlanteal surfaces of the 

 axis are convex ventro-dorsally, and they slope backward more than in the last-named 

 genus. 



The Humerus. — The head is unusually flat on the articular surface, the convexity 

 being mostly on the inner portion. The; lower portion differs both from the one described 

 by Scott as Ancodus brachyrhyncus and the one flgured by Kowalevsky as Diplopus 

 (1873, PL XXXVI, Fig. 4). The inner epicondyle is very uneven on the outer surface, 

 being covered with irregular ridges and depressions. It is much thinner than in 

 Hyopotamus and different in shape. Instead of being broad posteriorly to its lower 

 extremity it has a narrow border. The trochlea is also different. The median 

 ridge is almost as prominent as the inner one. The outer convexity is small and looks 

 like an accessory ridge on the median one. The inner groove is deep and the ridges are 

 not oblique. 



The Tibia. — The distal end is compressed antero-posteriorly, its transverse being 

 nearly twice its other diameter. The facets for the astragalus are very oblique, the inner 

 one being narrower and deeper than the outer. The outer edge of the tibia is angulate 

 to near the astragular facet, where there is a small oblique truncation. This evidently 

 was not for the shaft of the fibula, as that lay in the broad convexity anterior and internal 

 to the outer angle. 



The Fibula. — The lower end of the fibula is laterally compressed. Its antero- 

 posterior is twice its other diameter. There are on the outer side an anterior and a posterior 

 ridge and a smaller one on the plane surface between. The facet for the calcaneum is 

 oblong-oval or hastate, terminating posteriorly in a point. There is a posterior concave 

 surface and a smaller anterior convex one. The facet for the astragalus is different from 

 that of Diplopus (Kowalevsky, 1873, PI. XXXV, Fig. 3), being more like that of 



