EOTIIEKIUM iEGYPTIACUM. — EOSIREN LIETCA. 
209 
Width of skull-roof at lainbdoidal ridge 6-8 app. 
„ skull at middle of temporal fossa) 3'6 
„ skull between ends of supraorbital processes ... 15 app. 
„ snout in front of narial opening 6'2 
„ narial opening 4-8 
Length of dental series from canine to last molar .... 14'2 
The dimensions (in centimetres) of the molars arc : — 
Length. Width. 
m.\ 1-G 1-7 
m.2 1-8 1-9 
m.3 1-9 1-8 
The chief differences between this skull and that of Eosiren are: — (1) the occipital 
surface is wider and the lambdoidal crest more strongly developed ; (2) the supra- 
temporal ridges are less developed, so that the skull-roof is less clearly marked off from 
the temporal fossse ; (3) the cranial region is somewhat rounded; (4) the nasals are 
large, and must have overhung the nasal opening to a considerable extent; (5) the 
anterior incisors are not very much enlarged and have rather complexly folded crowms ; 
(6) the second and third incisors, though shifted back close to the premaxillary suture, 
are large and not displaced outwards ; (7) the canine is a large tooth on the alveolar 
border; (8) the palate is less narrowed between the anterior premolars. The arrange- 
ment of the nasals and the condition of the incisors and canines are the chief 
primitive characters noticeable. 
Mandible (PI. XX. figs. 2, 2 a). — In the mandible of Eosiren the downwardly turned 
symphysial region is greatly thickened, the anterior end of each ramus swelling 
out into a rounded bulbous mass, which, uniting with that of the opposite side, 
forms the massive symphysis. The line of union is marked ventrally by a deep 
groove [sym.). The large mental foramen {ni.f.) opens on the outer side of the 
symphysis, and is continued forwards by a deep groove to the extremity of the jaw. 
'fhe rami are comparatively narrow from above downwards ; their alveolar border 
is convex and their ventral edge concave, forming a regular arch from the symphysis 
to the lowest point of the enlarged and rounded angular region. The coronoid process 
arises from the outside of the ramus opposite the last molar which is in position, but 
in front of a posterior alveolus-like depression, which seems to point to the existence 
of a posterior successional tooth (see below). The upper portion of the coronoid 
process, the articulation, and the posterior portion of the angular region are broken, 
so that it cannot be seen whether any of the peculiarities described by Zigno in 
llalitherium {Prototberium) veronense existed in the present species. The large 
posterior aperture of the dental canal is situated on the inner surface of the expanded 
posterior region a little behind the posterior end of the molar series. Just within the 
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