PJiOZEUGLODON. 
245 
Z. osii'is occurs, and above that of Protocetus. Eocetus of Fraas also belongs to this 
horizon, and the large skulls and other remains mentioned by Ileadnell as occurring 
in the same locality may belong to that genus or to Z. isis. 
The material available for description consists of a skull with the right ramus of the 
mandible, the base of the skull, the posterior end, and right side of the palate being 
imperfect ; also portions of another skull and the three anterior cervical vcrtebra3 
in a beautiful state of preservation. 
Skull (PI. XXI. ; text-figs. 80-82). — The occipital surface is broad (PI. XXI. 
fig. Ic; text-fig. 81), and its upper portion is comparatively fiat, the lateral portions 
of the supraoccipital {soc.) which form the posterior face of the great lambdoidal crest 
not being reflected backwards at the sides as in Z. osiris ; the supraoccipital, in fact, 
is apparently flatter even than in the earlier Protocetm otavus, according to Fraas. 
Text-fig. 81. 
Posterior surface of skull of Prozeurjlodon atrox. 
hoc., basioccipital ; exo., exoccipital ; /.m., foramen magnum ; pa., parietal ; per., periotic ; 
soc., supraoccipital; scp, squamosal, g nat. size. 
The condyles (cond.) are relatively larger than in Z. osiris ; they are strongly convex 
from above downwards, and appear to have run down so that their narrow ventral 
portions are separated from one another in the middle line by a short interval only, 
and must have been formed in part by the basioccipital. Above the foramen magnum 
if-ni.) the exoccipitals {exo.) meet in a median suture, excluding the supraoccipital 
from the opening ; laterally they run out into a broad wing-like expansion, the upper 
edge of which unites with the posterior border of the squamosal {sq.), but laterally 
is separated from that bone by the intercalation of a strip of the mastoid portion of the 
periotic {per.), very • narrow above, but widening out below. This lateral expansion 
