ON SOME NEW AND LITTLE KNOWN CREODONTS. 
177 
ginated and the internal processes extend beyond the edges of the nares. The differ- 
ent species vary chiefly in the length of the portion enclosed between the frontals; 
this is greatest in H. horridus and least in H. leptocephalvs, where also the expansion 
at the fronto-raaxillary suture is least marked. 
The premaxillaries are shaped very much as in the dogs but are somewhat small- 
er, and have short nasal processes; the palatine plates are much reduced. The 
maxillaries are of great size; the two molar series diverge rapidly, so that the distance 
between the last molars is three times that between the first premolars; the alveolus 
projects far back and the palate is deeply notched on each side internally; the pala- 
tine processes of the maxillaries are slightly concave from side to side, and are 
nowhere very broad. 
The peculiar structure of the palate in Hycenodon has long been know. In 
H. horridus and H. crucians the hinder ends of the palatines are separated by a narrow 
fissure which gradually broadens, thus forming the narial opening. I have seen no 
specimen of H. cruentus in which the relations of those parts can be certainly made out, 
but from the structure of the portions preserved it is very probable that their condition 
is the same as in the species just described. In H. leptocephalus, as already mentioned, 
the posterior nares are brought very far back by the meeting of the alisphenoids and 
probably had no inferior opening at all. 
As in Thylacynus and many Insectivora the lachrymal has a considerable exten- 
sion on the face. The malar is rather slender, it is applied to the alveolar ridge 
rather close to the line of molars, but it does not form any portion of the anterior 
edge of the orbit which is occupied by the lachrymal; the malar arches outward from 
the maxillary, little if at all upwards; there is no post-orbital process. 
The mandible consists of a long slender horizontal ramus which gradually dee^)- 
ens posteriorly and forms a very long symphysis with its fellow. The differences 
exhibited by the various species are chiefly iu the ascending ramus. In U. horridus 
the coronoid is high and pointed, its hinder edge very oblique and its summit much 
in advance of the condyle; in II. crucians and leptocephalus the coronoid is much 
broader, its posterior edge is nearly vertical and almost overhangs the condyle; the 
masseteric fossa also differs in shape; in i/i cracmns it is rather shallow and most 
extended vertically, in the other species it is very deep and extends far forwards. H. 
horridus shows two mental foramina, the other species three; their position does not 
seem to be constant. In all the species the condyle is placed low, below the line of 
the teeth, and in all there seems to be an angular hook, though I have made it out 
with certainty only in H. cruentus. 
Foramina. M. FilhoD has described the foramina of H. hrachyrhyncus and 
states that the condylar foramen, foramen lacerum posterius and carotid canal are all 
' Filhol, M4m. sur quelques Mam. Foss., 1884, p 19. 
