THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 
but the posterior surface of the supraoccipital is deeply concave and overhanging 
and projects beyond the condyles much naore decidedly than in A. velaunus, show- 
ing a tendency to the formation of wing-like processes, such as occur in the oreo- 
donts. The anterior nares are small and have a less oblique position than in the 
European species, presenting more directly forward. The posterior nares open very 
far hack, the palatines being in contact for some distance behind the line of the 
molars and forming a narrow tube suggestive of aquatic habits. The tympanic 
bullm are decidedly larger than in any of the species figured by Filhol and of quite 
a different shape. The mandible has a higher coronoid process, of a shape entirely 
unlike that of any of the French species, more resembling that found in the rumi- 
nants, with a deep and regularly curved sigmoid notch; the masseteric fossa is 
deeply impressed. The size and shape of the coronoid process and the relative 
length and slenderness of the horizontal ramus of the mandible vary considerably 
in the different American species. 
The White River specimens of Ancodiis permit an exact determination of 
most of the bones of the skull, as the European ones do not. A careful description 
of these elements is by no means out of place, because the skull structure ol the 
Anthracolhcrium group is still little understood and much depends upon an 
accurate knowledge of it. 
The basioccipital is not broad, but heavy, and subcyliiidrical m shape, tapering 
soine>vl,at tmv«rd tlie anterior end. Near the eonJjle! no tubercles are developed, 
but a large pair, tvitli roughened surfaces and of oval shape, appe.y on the hone 
hot ween the auditory bulUe, and are separated from each other by a shallow groove. 
Oil the sides of the basioccipital are depressions to accoiinoodatc the laigel) in- 
III, ted Ivmpanios. The exoccipitals are low and very b,«d ; in the ‘ “ 
cerebeliar fossa form., a broad convexity, on each side ol winch ,s a sliallm do] Rs- 
.sioi, while the wide lateral portions are slightly concave n, the transverse direct,,,,,. 
Tlie'foi-aiiien iiiaomiiu is relatively small and of subcii-cular outline. R con ,y os 
•f . vriie Tut !!; no oreirt vei-lieal height, and they do no. pmject so ,n,,el, helow 
wmrd upon tubercles of the Uisioccip ^ suilliiie in shape; they stand 
The paroccipital processes are ruminan • j ^^^e not cm 
well in advance of and exterior te the “ f ij, to 
by ridges. wTh the tym. 
slender and elongate piismatic lo . 1 opening of the stylomastoid 
panic bullm at two points, between »>'■“' ^ the conriiiuation of 
Lramen. A gmove on the anterior ace « ^ , 3 „„„ri„r siirfaco is 
this canal. The supraoccipital is rat p^^power lateral depressions which 
concave m the middle, with two smaller the occiput is 
are separated from the Terhangs considerably behind the plane of 
htrirpoTlon „Ahe s- T,.e wlng-Uho processes 
