GENIOIIYUS MTEUS. 
ion 
Family SUID^E. 
The peculiar genus Geniohyus may be referred provisionally to this family, 
of -which it may be taken as representing a distinct subfamily, the Geniolujbm. 
Further knowledge of this remarkable form may lead to the establishment of a new 
family for its reception, but at present the course here adopted seems best. 
Genus GENIOHYUS, Andrews. 
[Geol. Mag. [5] vol. i. (1904) p. 160.] 
Known only from the mandible and lower teeth. The dental formula for the 
mandible seems to be i. 3, c. 'pm. 4, m. 3, but possibly the canine may be wanting, 
as will be explained below. The anterior incisors are enlarged and procumbent ; the 
premolars are all simpler than the molars, which are bunodont. The mandible bears 
on its lower border, immediately behind and beneath the symphysis, a pair of large 
backwardly-directed processes. 
Three species of this genus are at present known. 
Geiliohyus mirus, Andrews. 
[Plate XIX. tigs. 1, 1 a.] 
1904. Geniohjus mirus, C. W. Aiidrews, Geol. Mag. [5] vol. i. pp. 160-161, pi. vi. fig. 4. 
Type Specimen . — Symphysis and part of the right ramus of a mandible with the 
premolars and molars well preserved (PI. XIX. figs. 1, 1 a); Geological Museum, 
Cairo. 
This is the smallest of the three species, and at the same time the premolars are the 
simplest. Length of the premolar series is 5 cm. 
Form. & Loc. — Fluvio-marine beds (Upper Eocene) : north of Birket-el-Qurun. 
C. 8634. Symphysis and part o£ right ramus of mandil)le. Type specimen described and figured loc. 
cit. siqyra ; also PI. XIX. figs. 1, 1 A. The spout-like symphysial region is narrow both 
from side to side and from above downwards, and behind it, just where the rami begin 
to diverge, the ventral border of the jaw is produced downwards and backwards on 
either side into a long hackwardly directed process {pr.}, which is oval in section and 
probably ended in a point, hut the tip is broken away. The hinder border of the base 
of this process is connected with the lower edge of the horizontal ramus by a thin plate 
of bone. The ramus is incomplete ventrally, but was evidently narrow from above 
downwards. The function of the peculiar paired ventral process is uncertain. In the 
Dinocerata a somewhat similarly situated prominence on the mandible helped to protect 
