204 TBETIAEY VEETEBEATA OE THE FATtTM. 



available are in bad preservation and further material is necessary before any detailed 

 comparison with teeth of other genera is possible. 



Skull of Eotherium. — The skull and mandible of a primitive 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 Faytim remains were 

 obtained, and is probably the same as that in which was found the cast of the cranial 

 cavity which Owen made the type of Eotherium (Bgyptiacum. 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 

 fact 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 premaxillse 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.) axe produced downwards into strong paroccipital processes (pp.) 

 which extend below the level of the condyles ; there is a large condylar foramen 

 opening at the bottom of the groove between the base of the paroccipital process and 

 the occipital condyle. The sutures between the exoccipitals and basioccipital (hoc.) 

 are not clear, but that between the basioccipital and the basisphenoid (bsp.) is marked 

 by a transverse ridge, which crosses the basis craniiyi^t behind the level of the posterior 

 edge of the vertical plates of the pterygoids (pt.), which are closely united above with 

 the basisphenoid. Above the foramen magnum (f.vi.) the occipital surface is broad, 

 much broader than in Eosiren, and somewhat like the same region in Moeritherium (see 

 PL VIII. fig. 1 b). The supraoccipital (soc.) is gently concave from side to side ; its 

 upper border is greatly thickened and forms a great part of the 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 Sireneu cler mediterranen Tertiiirbildungen Oesterreichs," Abli. k.-k. gecl. Eeichsanst. vol. zix. pt. 2 

 (Vienna, 1904). 



