220 TEETIAET VEETEBEATA OF THE FAT^M. 



Pterodon africanus, Andrews. 



[Plate XIX. fig. 3; text-figs. 69-71.J 



1903. Pterodon africanus, C. W. Andrews, Geol. Mag. [4] vol. x. p. 342, fig, 3. 



Type Specimen. — Right ramus of mandible, incomplete posteriorly, with pm. 2-4 

 and m. 1-3 well preserved (PI. XIX. fig. 3) ; British Museum. 



This species is distinguished from all the others by its much larger size. 

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



M. 8503. Right ramus of mandible, wanting the posterior portion : pm. 2-4 and m. 1-3 in situ. 

 Type specimen figured loc. cit. supra. 



The symphysis, which seems to have remained unanchylosed through life, is very 

 deep and long, extending back to the level of the middle of pm. 3 ; its depth is largely 

 due to the enlargement of the front of the jaw resulting from the great size of the canine 

 tooth. Behind the symphysis the ramus increases very little in depth from before 

 backwards^ in which direction its lower border is gently convex. 



On the outer face o£ the jaw, in addition to two small apertures in the thickened wall 

 of the canine alveolus (c), there are three foramina: the smallest is in front beneath the 

 posterior half of pm. 2 ; the other two (m.f.) are larger and are beneath the anterior 

 lobes of pm. 3 and pm,. 4 respectively. 



The last molar (m. 3) is much the largest of the cheek-teeth ; it consisfs of a pair of 

 high compressed cusps which form a cutting-blade, the posterior lobe of which is con- 

 siderably the higher and has a sharp keel-like ridge on its postero-internal face ; the 

 small talon apparently consists of a single cusp with a sharp median ridge. There is a 

 small projection on the antero- external angle of the tooth near its base ; this seems to 

 belong to the cingulum, which is wanting elsewhere. The second molar (m. 2) is similar 

 to the first, except that the talon is relatively larger and forms a more distinct blunt 

 edge, and the small autero-external prominence is also larger. The first molar (m. 1) is 

 much the smallest of the series ; the two main cusps, which are considerably worn, are 

 less compressed and form a less trenchant blade than in the other molars. The talon is 

 similar to that of m. 2 and the antero-external projection is almost obsolete. The fourth 

 premolar {pm. 4) is much larger tlian the first molar : it consists of a large, conical, 

 somewhat laterally compressed and backwardly directed cusp with a cutting-edge; 

 behind this there is a small talon also with a cutting-edge in the same line with that 

 of the main cusp, and internal to it a sloping shelf-like surface. At the antero-internal 

 and postero-external angles of the tooth there are small tubercles belonging to the 

 cingulum, which is also slightly developed along the whole inner face of the tooth. 

 I'm. 3 is similar to pm. 4, except that the main cusp is not so high, the talon rather 

 smaller, and the antero-internal tubercle almost absent. Pm. 2 consists of a single 

 cusp, of which the anterior slope is shorter than the posterior ; just a trace of the talon 

 is still to be seen. Pm. 1 is represented only by its single nearly circular alveolus ; all 

 the other premolars and molars are implanted by two roots. The alveolus of the 

 canine (c.) shows that that tooth was very large and oval in section, the long axis being 



