M EGA LOl r Y RAX M IN( ) R 
07 
Form. & Loc. — Fliivio-inarine Reds (Upper Eocene) : iiortli of Birket-el-Qurun. 
Upper Dentition (PI. YU. fig. 1). — Exce])t in tlieir smaller size the upper molars 
of this species closely resemble those of M. eoewnns, the only notable differences being 
the absence of the small accessory styles of the outer face of m. 1 and m. 2, and the fact 
that the main outer cusiis form slight projections on the ectoloph. The premolars, on 
the other hand, differ more considerably from those of the larger species, the chief point 
of difference being that they are more simple. Thus in pm. 4 there is a fairly well- 
developed postero-internal cusp, but it is smaller than in the corresponding tooth of 
M. eoccenus, and the tooth is less quadrate in outline. l\\pm.?i the postero-internal 
cusp is practically absent and its position is occupied by a shelf-like projection ; the 
same is the case with the other premolars. In pm. 1 the antero-internal cusp also is 
much smaller than in M. eocamus, and approximates in form to the canine of that 
species. In fact, each of the premolar teeth of the present species resembles the next 
tooth in front of it in M. eocceniis, rather than the corresponding tooth. 
It can be seen that the posterior border of the zygomatic process of the maxilla is 
about opposite the hinder lobe of m. 3. 
Lovoer Dentition (PI. VII. figs. 2, 3). — The collection at Cairo includes portions of 
the right and left rami of a mandible which probably belongs to this species and 
possibly to the same individual as the type specimen. The portion of the left ramus 
preserved contains the two anterior incisors (fig. 3, I, i. 2), the third and fourth 
premolars, and the first and second molars. The right half (figs. 2, 2 a) includes 
the three posterior premolars and the molars. Unfortunately, the two rami do not 
join, some fragments of bone being wanting, and in the left ramus the alveolar 
border is incomplete between the second incisor and the third premolar, so that the 
exact dental formula cannot be determined. The incisors (fig. 3), of which, probably, 
only two pairs were present, are of somewhat peculiar form, and in the present 
specimen they are considerably worn. The crowns are broad and spatulate, and 
in the case of the anterior one [i. I) somewhat flattened on the anterior face. 
The Avear-surface in each forms a narrow band along the whole of their upper 
edge. They show no trace of the peculiar pectinate form seen in the incisors of 
the recent Hyraces, but it is by no means impossible that this may have existed in the 
unworn tooth. 
The cheek-teeth (fig. 2), so far as known, form a closed series. The molars consist 
of two crescents : the postero-internal end of the anterior crescent terminates in a 
cusp [ai.) which is joined posteriorly with another small cusp, which partly closes 
the opening of the posterior crescent. This cusp is the metastylid [msd.), and is 
strongly developed in all the teeth from the third premolar back. In pm. 2 it is not 
present. The third molar has a small talon {t.) giving a crescentic surface in Avear. 
The cingulum is fairly Avell developed on the outer side of the last premolar and 
in the molars. 
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