EOSIREN LinYCA. 
201 
border of the narial ojiening. This aperture is an elongated oval in outline, its long 
diameter being about twice its width. In front of it the upper surface of the rostrum 
is broad and rounded from side to side, but towards its extremity it becomes compressed 
and its upper border forms a sharp angle. At the end of the premaxillae there is a pair 
of large though comparatively shallow sockets for the enlarged incisors (/. 1), separated 
by a thin wall of bone. Behind and beneath these the alveolar border forms a sharp 
edge continuous with that of the maxillae. The palatal surface of the premaxillae is 
strongly arched and posteriorly forms the roof of the large anterior palatine foramen 
(Bl. XX. tig. 1 A, a.jp.f.), the lower border of which, as already mentioned, is formed 
by the anterior edge of the maxillae. Posteriorly the palatine foramen opens into the 
narial cavity ; its form and relations differ somewhat from those of the same opening 
in Manatus^ Ilalicore, and Rhfjtina. In Manatus the palatal portions of the premaxilhe 
are scarcely at all developed ; in Ilalicore they are in the same plane as, and unite 
with, the palatine plates of the maxillae, the lateral borders of the elongated anterior 
palatine foramen being formed equally by the twm bones. In Rhijtma the elongated 
foramen is almost entirely enclosed by the premaxillae ; in the present genus it 
approximates much more nearly to the condition seen in Halitherium, in which, 
however, the palatine region of the premaxillee is rather less developed. 
The vomer seems to be much like that of Halitherium, as figured by Lepsius ; it is 
deeply grooved and the nasal opening must have been divided, at least posteriorly, by 
a vertical cartilaginous septum. 
In all the specimens the zygomatic arch is broken and incomplete. Judging, 
however, from an imperfect specimen, it appears that the structure was much as in 
Halitherium, the zygomatic process of the squamosal forming a broad blade, the lower 
edge of which is underlain by the backward process of the jugal. This latter 
widens out in its middle region and bears a downwardly-directed blunt process, as 
in Halitherium. The body of the squamosal forms a considerable portion of the side 
wall of the cranium. Posteriorly it unites with the supraoccipital above and perhaps 
for a short distance below this with the exoccipital ; but for the most part it is separated 
from the latter bone by the mastoid portion of the periotic, which is exposed on the 
occipital surface as an elongated convex mass. In front of its union with the mastoid 
the squamosal bears a strong rounded ridge, forming the outer portion of the lambdoidal 
crest. In front of this there is a concave surface bounded in front by the ridge marking 
the origin of the zygomatic process. 
The base of the skull is for the most part wanting ; in the type specimen, however, 
it can be seen that the basisphenoid and presphenoid were both much thickened and 
that the former is embraced by the upper ends of the massive pterygoids. 
The cast of the brain-cavity (text-fig. 65) is of considerable interest. The olfactory 
lobes [ol.) are small and situated low down. The hemispheres are divided from one 
another by a very deep groove in front, and each is divided into a swollen anterior 
2 D 
