Arrangement of the Fossil Kangaroos, 207 



classification cannot be attempted ; and it is much to be re- 

 gretted that the author had so little material a1 his command 

 at the time. Since the work was published, Professor Owen 

 has received numerous additional proofs, through his chief 

 contributor and friend, Dr. George Bennett, and amongst these 

 at least a dozen fragments of skulls, with the incisors perfect 

 or nearly so. The grinding-series ditfers much in some gi'oups ; 

 and seldom can a pair of skulls be found which have the teeth 

 alike. The grinders are always subject to more than the usual 

 variation ; and for this purpose large quantities of skulls were 

 brought together and examined here before classification was 

 attempted. The result led to the conclusion that by the upper 

 front teeth only (of half-gi'own or almost adult individuals) 

 can skulls be named with certainty. There are two kinds of 

 third upper incisors which occur with premolars of a certain 

 form ; and this sanctions the division into two large groups as 

 above, with the following additional characteristics. 



1. Macropus. 



With a broad third upper cutting-tooth (without a fold or 

 groove when adult), with deciduous premolars, and subject to 

 shedding the grinders up to a single pair in each ramus in 

 old age. 



2. Halmaturus. 



With rather naiTOw and grooved third upper incisors and a 

 more permanent dentition, the gi'inders ]:>eing worn down but 

 seldom shed. Besides this distinguishing point, the distance 

 between the lower incisor and the premolar must be considered ; 

 and the wider this space, the sooner the teeth are reduced in 

 number ; the shorter, the longer are the grinders retained. 



Compare this space in a wallaby's jaw with that of a kan- 

 garoo, and the difference will be understood at once. A long- 

 headed kangaroo sheds the giinders, whilst a short-headed 

 wallaby wears them out. 



To illustrate this it is necessar}'- to refer to the author's 

 splendid illustrations. On plate xx. we have a long-headed 

 kangaroo (under fig. 1), certainly with a short upper third in- 

 cisor, but with every indication that the grinders will be shed 

 with age and not worn down. Figures 13 and 15 represent 

 similar animals, who shed their teeth; but Xo. 11 (a rock- 

 wallaby's lower jaw) belongs to the " grinding-down " section, 

 and in this the space between incisors and molars is very short. 



On plate xxiv. (figures 10, 11, and 12) the lower den- 

 tition of our black wallaby is given. The wear of the incisor 

 below, and the corresponding teeth above, shows that the 

 animal was fully adult, but had not shed the premolar, as tme 



