106 FOSSIL JAWS OF MACROPODID^], 



from 33-1 to 39-9 (5); of the first two from 21-5 to 27-4 (7); of 

 m.-^ m.3 from 28-0 to 34-1 (11); of m.^ 17 (1); of m.^ from 17-0 

 to 18-4 (6); and of m.* 16-6 (1). The breadth of the palate is 

 from 66-0 to 68-5 (2). 



In young: p.'^, nip.'^, m. ^ range from 28-6 to 37*0 (3); mp.^, 

 m.\ m.2 41-7 to 44-4. 



The proportionate mean widths of m.'^ above and below are 

 11-8 and 13-6. 



The degree of variation in the lenoth of the cheek-teeth found 

 in this species is less than that shown by H. ruficoUis; and the 

 premolar has a more restricted range of length than in most of 

 the larger existing wallabies. On the other hand, the width of 

 the teeth and the depth of the mandible have a somewhat greater 

 range of measurement than in living species, and in thickness the 

 ramus is decidedly more variable. But as in all the dimensions, 

 the extremes are reached by insensible gradations, excess even in 

 the width of the teeth must be considered a peculiarity of the 

 sjDecies and one probably related to its inordinate vigour as shewn 

 in its fecundity. It is quite the most abundant Macropod of its 

 period. 



As no one of the several species added by Owen to the type of 

 his genus Pr<jteuinoihn has a destinctive character other than a 

 supposed differentiation in size, Lydekker has taken a step in the 

 right direction in reducing their number to three — bi^ehus; rcechus 

 and aiiak. With a fuller supply of material he would no doubt 

 have felt perfectly safe in referring all the fossils of the Protem- 

 nodont series to the single species anah. The essential unity of 

 the species is shown not merely by graduation of difference affect- 

 ing each part of each of three hundred and thirty individuals 

 alike, but by that disproportionate difference between the parts 

 which renders it impossible to lay down interspecific lines of 

 demarcation anywhere. Detailed measurements of thirty-four 

 entire mandibles of brehus, rcechus and anak, and a careful com- 

 parison of their differences with those observed in the measurement 

 of recent species fail to show that there is any sufficient reason 

 for regarding them as distinct species. Constant differences of 

 form there are none. 



