170 
TEETFAliY VEliTEBEATA OF THE EAYCM. 
Plliomia serridens, Andrews Sc Bcadnell. 
[Plate XVJII. figs. 4, 4 a.] 
1902. Pltiomm serridens, Andrews & Eeadnell, A Pi-eliniinary Note on some new Mammals from 
the Upper Eocene of Egy})t, ])p. 1-5, figs. 1, 2 (Survey Dept., Cairo). 
1005. Falwomaslodon, juv^, Sclilosser, Neues Jahrb. £. Mineralogie, etc. vol. i. pt. i. (Referate) 
p. 157. 
Type Specimen . — Anterior portion of left ramus of mandible Avitli incisor and two 
cheek-teeth, figured and described loc. cit. supra, also PI. XVIII. figs. 4, 4 a ; 
Geological Museum, Cairo. 
4'he type and only known species, with mandibular symphysis G'5 cm. in length. 
Form. & Log. — Fluvio-marine beds (Upper Eocene): north of Birket-el-Qurun. 
The mandibular ramus (PI. XVIII. figs. 4, 4 a) upon winch the species is founded is 
incomplete posteriorly. The symphysial region {sym.) is very long and deepens consider- 
ably from before backwards ; the upper surface with its fellow of the opposite side must 
have formed a spout-like groove, while the ventral surface is strongly convex from side 
to side and to some extent also from before backwards. Behind the symphysis the 
ramus of the jaw arches outwards, its outer surface being convex from before back- 
wards and also from above downwards ; the inner surface is concave in the former 
direction and nearly flat in the latter. There are two foramina on the outer face: 
one, the larger of the two, is just behind the socket of the incisor ; the other is beneath 
the anterior end of the second of the cheek-teeth in situ. The bone shows traces of 
the peculiar fibrous appearance characteristic of many young bones, a circumstance 
which tends to support Schlosser’s view as to the nature of the specimen. 
The incisor [i. I) is of very peculiar form. Its inner border, where it is in contact 
with its fellow of the opposite side, is straight. The outer edge is conve.v in front and 
is marked by a series of crenulations (about five in number). The upper face of the 
tooth is concave from side to side, the ventral convex with two or three sliglR 
longitudinal ridges. The tooth thickens rapidly towards its base. The enamel 
covering is confined to the end of the crown; it is found on both the upper and 
lower surface ; on the outer side it extends back as far as the last of the denticulations, 
and on the inner not quite so far. The incisors must have formed a S])out-like 
continuation of the symphysis, much as in Fahvomastudon. The great size and increase 
in thickness of these teeth towards their base make it difhcult to regard them as 
belonging to the milk-series ; on the other hand, if they are the permanent incisors, 
they could never have attained the size of those of ]\ila'omastodon hcadneUi or 
winfoni, so that if this animal was a Palceomastudon it must have been quite a small 
species. 
