4;)6 PTT:r..u.orF.x. 



tlioiij;li i\w. dt'iititioii of tliis geims is, it presents in fact scarcely a 

 single ehuracter -wliioh is not either developed to a certain extent 

 or at least distinctly Ibreshadowed in Pti-ropns ■psi'laphon, pi/o.sws, 

 inhcrcvlatiis, or Jmcojiterus. The only essential modifications re{juired 

 to transform the dentition of those species into that of 1 ieraJopex 

 are: — (1) a rather slij;ht further increase of the size of the upper 

 incisors and somewhat stronger development of their cingula 

 (upper incisors larger and cingula stronger than usual in the 

 vselaplion group); (2) a considerable enlargement of i„ (a re- 

 markable enlargement has already taken place in the p>seUip]ion 

 group, i., being as much as five times tlie bulk of i^ ; cf. also the 

 related Jomhocensis and samoi-nsis groups); (3) a considerable 

 increase of the bulk of the upper canines combined with an 

 enlargement of the inner basal cusps and the posterior marginal 

 cusp (canines already in Pt. psdaplion and some allied species 

 unusually stout with margin of cingulum broken up into separate 

 tubercles, these latter in Pt. pilosus exactly similar in number and 

 position to those of Ptcralope.v\ a small posterior marginal cusp 

 already present in Pt. tubercnJattis) ; (4) a relatively slight further 

 enlargement of Pj (considerably enlarged in most species of the 

 2}seJiiphon group ; (/. also the samoensis group) : (5) a conspicuous 

 shortening and broadening of the upper molariform teeth and 

 stronger development of their posterior and anterior basal ledges 

 (to the shortening of these teeth there is a parallel in Pi. lenm- 

 jitcnis; in all species of the pscJaplwn and sfl)}(oej<s/s groujis the 

 posterior basal ledges are unusually heavy, in all the anterior 

 ledges at least distinctly indicated, and in one, Pt. lencoptems, 

 scarcely less developed tlum in the more primitive species of 

 Fteralopex, viz. Pt. anceps); (C) a transverse depression or notch 

 in the cutting-edge of the outer longitudinal ridge of p^, mj, and 

 m.„ ])roducing a more or less distinct, but never complete, splitting 

 of tlic ridge into two cusps (a similar depression or notch develojjcd 

 in the inner ridge of m^ of Pt. ■pseJaplnm, and both in inner and 

 outer ridges of m^ and m^ of Pt. leucnpterus). — In general shape the 

 skull of IHeralope.v closely approaches that of Pt. pselaphon and 

 allied species ; such (relatively slight) modifications as have taken 

 place are, probably M'ithout exception, consequences of the ex- 

 tremely heavy dentition and the correspondingly increased size and 

 strength of tlie muscles which direct the movements of the lower 

 jaw, viz. tlie temporal muscles (very high sagittal crest, long 

 postorbital jirocesses, heavj' zygomata, very broad coronoid), the 

 masseter (well-marked horizontal ridge along anterior third of 

 zygoma near its lower margin, very heavy angular process of 

 mandible, condyle very high above alveolar margin, unusualh- 

 prominent masseteric crest from condyle vertically downward to 

 lower margin of angular process), and pterygoid and digastric 

 muscles (large ectopterygoid, post-tympanic, and paroccipital pro- 

 cesses). — The only noteworthy external characters of Ptcrahpex 

 are those given in the diagnosis and descri])tion of the genus, viz. 

 the origin of the membranes from the spinal line (to this there are 



