204 
TERTIAEY VERTEBEATA OF THE EATtM. 
uvailable are in bad prc'servation and further material is necessary before any detailed 
comparison with teeth of other genera is possible. 
SliuU, of Eotherinm. — The skull and mandible of a ])rimitive Sirenian from the 
limestones of the Mokattam Hills has recently been acquired by the Geological 
Museum in Cairo and is important for comparison with Eosiren. The horizon from 
which these specimens come is lower than that from which the Fayum remains were 
obtained, and is probal)ly the same as that in which was found the cast of the cranial 
cavity which Owen made the type of EotJieniim wgyptiacnm. This skull and mandible 
may in fact be referred to Owen’s species, though in some respects it differs from the 
brief description of some new material of that Sirenian lately published by O. Abel *. 
When this author has published his complete account of the Egyptian Eocene Sirenia 
it will no doubt be possible definitely to determine these specimens ; meanwhile the 
tact that they represent a more generalized form than Eosiren, and are from a lower 
horizon in the same region, is sufficient to justify the comparison of the two ty[)es. 
The skull in question (text-fig. 66) is nearly complete, but the anterior portion has 
been compressed in such a way that the rostrum has been straightened, instead of 
bending down as, judging from the mandible, it must have done in the living animal ; 
the anterior ends of the premaxillm have been separated by a fracture, the result 
of which is that this region has the appearance of having been more elongated than 
was actually the case. 
The occipital condyles are very large and are more sessile than in Eosiren ; in the 
mid-ventral line they are separated by a sharply defined notch. Laterally the 
exoccipitals (exo.) are produced downwards into strong paroccipital processes {g)}).) 
which extend below the level of the condyles ; there is a large condylar fi)ramen 
opening at the bottom of the groove between the base of the paroccipital process and 
the occipital condyle. The sutures between the exoccipitals and hnsioccipifal [hoc.) 
are not ch ar, but that between the basioccipital and the hasisgjlumoid [hsp.) is marked 
by a transverse ridge, which crosses the basis cranii]o%i behind the level of the posterior 
edge of the vertical plates of tlie pterygoids [l^t.), which are closely united above with 
the basisphenoid. Above the foramen magnum [f.m.) the occipital surface is broad, 
much broader than in Eosiren, and somewhat like the same region in Mceritheriani (sec 
FI. VIII. fig. 1 b). The snpraoccipital (soc.) is gently concave from side to side; its 
upper border is greatly thickened and forms a great part of tlic massive lambdoidal ridge. 
In the middle line in front it thrusts a blunt triangular process between the posterior 
ends of the parietals ; laterally its upper angles form prominent backwardly directed 
bosses of bone, to the anterior face of which the parietals are closely united. The upper 
* “ Die Sirenen der inediterraTien TertiiirbilJungcii ()e.sterreiflis,” Abli. k.-k. geol. Eeiebsanat. vof. xix. pi. 2 
(Vienna, 1904). 
