170 TEETIAET VERTEBEATA OF THE FATtM. 



Phiomia serridens, Andrews & Beadnell. 

 [Plate XVIII. figs. 4, 4 A.J 



1902. Phiomia serridens, Andrews & Beadnell, A Preliminary Note on some new Mammals from 

 the Upper Eocene of Egypt, pp. 1-5, figs. 1, 2 (Survey Dept., Cairo). 



1905. Palceomastodon, juv., Schlosser, Neues Jahrb. f. Mineralogie, etc. vol. i. pt. i. (Referate) 

 p. 157. 



Ti/pe Specimen. — Anterior portion of left ramus of mandible with incisor and two 

 cheek-teeth, figured and described loo. cit. supra, also PI. XVIII. figs. 4, 4 A ; 

 Geological Museum, Cairo. 



The type and only known species, with mandibular symphysis 6"5 cm. in length. 



Form. & Log. — Fluvio-marine beds (Upper Eocene) : north of Birket-el-Qurun. 



The mandibular ramus (PL XVIII. figs. 4, 4 a) upon which 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. 1) 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 convex 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 slio-ht 

 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 spout-like 

 continuation of the symphysis, much as in Palceomastodon. The great size and increase 

 in thickness of these teeth towards their base make it difficult 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 Palceomastodon headnelli or 

 wintoni, so that if this animal was a Palceomastodon it must have been quite a small 

 species. 



