574 MR. R. LYDEKKER ON LOWER JAWS OF PROCOPIODON. 



the molars and the ascending ramus. Moreover, the surface of the 

 jaw external to the last molar is separated from the surface above 

 the " angle " by a much less sharply defined ridge than that which 

 occurs in P. Ilapha. An imperfect but rather larger right mandibular 

 ramus (B. M. No. M. 1897) is figured by Owen in the Phil. Trans, for 

 1874, pi. Ixxx. figs. 1, 2, where it is referred to P. Goliah. The 

 dimensions of these two specimens are as follows : — 



Bingera sp. No. M. 1897. 



inches. inches. 



Length of last 2 molars 1*8 1*83 



„ „ „ 4 ,, ^ 3-45 



„ „ cheek-series 3*55 



Greatest depth at symphysis .... 1*9 1*85 



J, width of jaw 1*75 



It may be added that the immature mandibular ramus figured iu 

 the Phil. Trans, for 1874, pi. Ixxx. fig. 7, and referred to P. Goliah, 

 differs from the specimens described as P. llajpha by the greater 

 antero-posterior length of the fourth premolar, which is seen in 

 alveolo. 



The foregoing description leaves therefore no doubt as to the exis- 

 tence of two large-sized species of Procoptodon in the Australian 

 Pleistocene, which are markedly distinguished from one another by 

 the characters of their lower jaws. Both species were subject to 

 considerable variations in size, which may have been either sexual 

 or racial. Since the stouter and deeper type of jaw has been referred 

 to the species described as P. Raplia, while one mandible of the more 

 slender type has been described as P. Goliah, it seems advisable to 

 allow these two types of mandible to be so named, until we obtain 

 decisive evidence as to which really belongs to P. Goliah ; if, indeed, 

 the type of that species affords any characters by which it can be 

 distinguished from the second species. The possibility that the types 

 of those two species are really specifically identical must also be 

 borne in mind ; and if this should prove to be the case the name P. pusio 

 might be the one which would have to be adopted for the second 

 species. Here, however, the uncertainty again arises as to whether 

 the type of that species indicates a small race of P. Goliah or of the 

 second species. 



EXPLANATION OF PLATE XXL 



Fig, 1. Inner view of the left ramus of the mandible of Procoptodon Eapha. 

 2. Inner view of the right ramus of the mandible of Procoptodon Goliah. 

 2 a. Aperture of masseteric fossa of ditto. 

 26. Oral aspect of last two molars of ditto. 



a7i. angle of mandible ; ca. aperture of dental canal ; sy. symphysis ; p. 4, 

 premolar ; m. 1^, molars. 



With the exception of fig. 2b, which is \, the figures are ^ nat. size. 



