220 
TERTIARY VERTEJ3RATA OF THE FAYOM. 
Pterodon africanus, Andrews. 
[Plate XIX. fig. 3 ; text-figs. G9-71.] 
It'O,”). Plerndo)! aj'r/rainis, ( !. W. Andrews, Geol. iMag. [4] vol. x. p. 342, fig. 3. 
S,j)ccimm . — Rigid ramus of mandible, incomplete posteriorly, with 2-4 
and m. 1-3 well jweserved (PI. XIX. fig. 3) ; British Mnseum. 
'1 Ids species is distinguished from all the others by its much larger size. 
Form. cC* Loc. — Fluvio-marine beds (Upper Eocene) : north of Birket-el-Qurun. 
M. 8503. Right rainns of mandible, wanting the ])osterior portion : pm. 2-4 and rn. 1-3 vi situ. 
Type S{)ecimen figured loc. cit. sitjo'd. 
The symphysis, which seems to have remained nnanchylosed throngli life, is very 
deep and long, extending hack to the level of the middle of ]>m. 3 ; its depth is largely 
dne to the enlargement of the front of the jaw resnlting 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 of the jaw, in addition to two small apertures in the thickened wmII 
of the canine alveolus (c.), there are three foramina; the smallest is in front beneath the 
))Osterior half of pm. 2 ; the other two (m.f.) are larger ami 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 consists of a ])air of 
high comprcsseil cusps which form a cutting-blade, the ])osterior lobe of which is con- 
siderably the higher and has a sharp keel-like ridge on its postero-internal face ; the 
small talon a])parently consists of a single cusp with a sharp median ridge. There is a 
small ])roj(‘ction 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 (»?. 2) is similar 
to the first, except that the talon is relatively larger and forms a more distinct blunt 
edge, and the small antero-external prominence is also larger. The first molar (m. I) is 
mnch the smallest of the series ; the two main cusps, wdiidi are eonsiderably worn, are 
h‘ss 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 {jmi, 4) is much largx'r than the first mohu’ : it consists of a large, conical, 
sounnvhat laterally com])r(^ssed and backwardly directed cus]) with a cutting-edge; 
behind this there is a small talon also with a eutling-edge in the same line with that 
of the main cusj), and intc'rnal to it a slojiing sludf-like surface'. At tlue antc'ro-internal 
and postero-external angles of thee tooth tlu'iae are small tuberches belonging to thee 
cingulum, whidi is also slightly developc'd along the' whole' inner lae;e e)l the te)olh. 
I*m.?) is sinular te) pm.-\:^ esxeu'pt that the' main cus[) is ne)t se) high, the tale)n rather 
smaller, ami the ante-ro-inteiaial tube'rehi alme>st ab.-e'ut. Pm. 2 consists of a single 
cusp, of whieh thee anterieer shepe' is sheeideu’ than thee pe)ste'rie)r ; just a ti’acee e)t the tale)n 
is still to be seeen, /’m. \ is i’e'|)rcseente'd e)nly by its singlee neearly cireidar alveolus; all 
thee other jere'molars ami meelars are imjilanie'd by twe) reeeets. The alveolus of the 
canine (c.) sinews that that tooth was ve'ry lai’ge anel oval in se'ciion, the long axis be'ing 
