CKEODOi>ITA. 
91 
an extensive transverse articulation with the carpus, and an external tuber¬ 
osity relatively little produced. The external ridge of the shaft of the 
femur is developed into a protuberance, which is a low third trochanter. 
In the tibia, the trochlear surface is oblique and nearly uninterrupted, much 
as in Oxycana, and without the grooves for an hourglass-shaped astragalus, 
as in Mesonyx. 
This genus resembles Hycenodon in the structure of its superior molars. 
* It differs in the inferior molars, especially in the existence of a tubercular 
heel of the antepenultimate and penultimate, and probably in the arrange¬ 
ment of cusps on the anterior part of the latter. 
Ambloctonus sinosus, Cope. 
Pl.ate xxxiii. 
System. Cat. Yert. Eocene i^^ew Mexico, U. S. Geog. Survs. W. 100th M., 1875, p. S. 
Two imperfect skeletons rejjresent this species in the collections of the 
Survey. The best preserved includes the right maxillary bone, with crowns 
and roots of the last four molars. The first of these is wider behind than 
before, the posterior root being double. The next has a triangular crown, 
with the exterior and anterior borders at right angles to each other, and of 
subequal lengths. The fourth tooth is not quite so wide, but about as long 
as the one just described, has thre'e lobes of the outer summit, and a con¬ 
vex anterior border. The interior heel of the first molar is constricted at a 
])oint of its border, indicating an additional internal cusp, probably basal. 
The foramen infraorbitale is remarkably large. Owing to the state of the 
specimen, the number of preniolars cannot be ascertained. The canine is 
worn almost to the alveolar border in a vertical truncation; the diameter 
of the alveolus for the third or outer incisor is but little less than that of 
the canine. 
The characters of the three last inferior molars may be partially 
determined from the two individuals. The last molar is smaller in the 
specimen already partially described than the two which precede it, and 
which are subequal. It has a very short heel, with a cutting-edge on the 
outer side. The remainder of the crown is subtriangular in section at the 
base, supporting a posterior and an anterior tubercle, which are connected 
on their inner sides by a cutting-edge. There is a cingulum on the internal 
