9 
TEliTIAliY VEETEBRATA OF THE EAYtTM. 
family ARSINOITHEllIID.^:. 
Comprising only the genus Arsinoitherium, and not yet precisely definable. 
Genus ARSINOITHERIUM, Beadnell. 
[Prelim. Note on Arsinoitherium zitteli, Beadn. : Survey Dept., Cairo, 1902.] 
Occipital surface of skull strongly inclined forwards ; a pair of small frontal 
horns over the orbits, and a pair of enormous nasal horns arising from a common 
base constituted by the nasals and frontals. In the adult, a prenasal bar of bone 
uniting the anterior border of the nasals with the premaxillae. Orbit open posteriorly. 
Palate strongly arched from side to side. Molars bilophodont. Neck very short. 
Humerus and femur considerably longer than the radius and tibia respectively. 
So far as known, this genus is represented by two species only in the Upper Eocene 
of Egypt. Nearly all parts of the skeleton have been discovered. 
Skull (Pis. I., II., III. ; text-figs. 1-4). — The skulls in the collections belong to 
individuals of various ages, ranging from young animals in which the last molar is still 
uncut and most of the sutures remain open (PI. III. fig. 2) to fully adult individuals 
with the last molar much worn and almost all the sutures obliterated (Pis. I., II.). An 
intermediate condition is shown in PI. III. fig. I, where the last molar is just coming 
into wear, and some of the sutures {e. g. that between the exoccipital and squamosal) 
are still open, while the horns are rounded and the character of the bone shows that 
growth was actively proceeding at their summit. An adult skull in the British 
Museum (Pis. I., II.) suffices for the greater part of the general description, and 
this specimen is important because it was found in actual association with its 
mandible. 
The general appearance of the skull is most remarkable. Seen from behind (text- 
fig. 1) the most notable characters are: — (1) The large size and great prominence of 
the occipital condyles ; (2) the extreme inclination forwards of the occi])ital surface ; 
(3) the great development of the lambdoidal crest, the lower ends of which form strong 
prominences in the adult animal. In a front view (PI. II. fig. I a) the appearance 
is very curious, the two great horns and the sharp wedge-shaped extremity of the 
snout giving the whole a triradiate form. Beneath the base of the horns are the 
two very large narial apertures, divided in the adult by a vertical prcnasal bar 
of bone. An upper view of the skull (PI. III. fig. 2) shows the large widely- 
separated and prominent condyles, the forwardly-inclined occipital surface, and in 
