CORYPHODON. 
231 
entirely distinct. A low ridge or angle extends forward from each of them, 
and unites with its fellow on the middle line opposite the auricular meatus. 
The median ridge thus formed disappears at the sphenoid cross-suture, and 
here there exists on each side a low tuberosity which is equally transversely 
divided by the suture. A little anterior to this point, the external inferior 
margin of the basisphenoid is produced downward and forward into a short 
longitudinal crest, whose anterior base is pierced by the foramen ovale. 
The mandibular rami are preserved excepting the posterior portions, and 
support all the teeth. They are rather shallow, and exhibit the usual 
upward concavity of the inferior border at and behind the last molar tooth. 
The inner face is flat, the external convex. The symphysis is elongate, 
reaching to the posterior border of the second inferior premolar. 
The teeth are all preserved, and in good condition. They are but 
little worn, and the last molars in both jaws have their posterior portions 
not fully protruded. The last superior molar has the usual strong anterior 
cingulum, but none on the external and internal borders of the crown. 
The anterior cross-crest is concave backward, and the posterior cross-crest 
is similarly concave. 'J'he anterior crest at its inner end sends a crest 
downward and backward, which becomes a posterior basal cingulum. This 
forms an angular protuberance opposite the middle of the posterior crest, 
and there terminates. This is different from the arrangement in C. radians, 
where this descending cingulum rises again, and is continued upward into 
the anterior extremity of the posterior crest. In the penultimate molar, the 
posterior V is large and wide, and without external basal cingulum; the 
anterior V is represented by a conic cusp, little distinct from the border of 
the posterior. The anterior cross-crest is very prominent, both externally 
and internally; its inner extremity rises into a broad obtuse cusp, which is 
also the termination of a strong cingulum from the posterior side of the 
crown. Besides this, there is a strong, anterior basal cingulum, but none on 
the inner side. The antepenultimate molar is considerably smaller than 
the penultimate, but is generally like it except in the better development of 
the anterior external V, which is flat externally and convex internally. The 
premolars display the usual characteristic of a single external V rising to 
