14,i DK. B. A. EEXSLET OX THE EVOLUTIOIS' 



continuing in the Macropodiu^e, and have in all probability originated independently 

 from pbalangerine forms possessing the same peculiarities. The extinct form Bnrramt/s, 

 described by Broom ( 1 8 96 ), is a member of the same general series, although, as mentioned 

 by that writer, its positiou cannot be exactly determiaed at present bsyond that it 

 presents phalangerine as well as macropodine resemblances, and that it is not directly 

 ancestral to Eypsiprymnodon. 



The special evolution of the group is chiefly marked by the progressive modifications 

 of the molars and sectorial premolars, the canines and incisors retaining for the most part 

 primitive relations throughout. The various forms, with the exception of Bettongia 

 cuniculus, appear to be related in the following order : — Iltipslpry^nnodon moschatus, 

 Bettongia penicillata, B. Gaimardi, B. Lcsueuri, and yEpyprgmnus rufescens. B. cuni- 

 culus appears to represent a side development of B. penicillata, or possibly B. Gaimardi. 



Sequence of Molar Patterns. — The progressive characters noticeable in the molars are 

 as folloAvs : — [a) tendency towards reversal of the relative proportions of the three 

 anterior teeth above and below ; [b] rotation inwards of the postedor ends of the tooth- 

 rows ; (<?) slight hypsodontism of the crowns. 



In the most primitive form, Ilypsijiry m,nodon moschatus, the first and second upper 

 and lower teelh are approximately equal ia size, while the third are slightly smaller than 

 the second and the fourth smaller than the third. Tlie tooth-rows are straight, as in 

 some of the Phalangerinte. The teeth are quadrituberculate and brachybunodout, as in 

 llie latter "roup. In the upper teeth the protocone aud hypocone are placed oa a level 

 with the outer cusps, and tlie internal sides of the latter elements toad to form low 

 transverse rido-es, both as in the Phalangerinaj. There are no triices of external styles. 

 The last upper molar is triangular, as in the Phalangeriaae, but its posterior lobe shows 

 indications of division into two cusps. Ia the lower molars the inner cusps, like the 

 outer cusps of the upper teeth, show indications of the development of low ridges. As 

 in the advanced Phalaugerime, the first lower molar has hut one cusp on its anterior 

 lobe. 



Passin"" throu"-h the remaining members of the series we find these characters 

 chanoin"- as follows : — The second teeth from being equal in size to the first in Rypsi- 

 pripnnodoH and in some specimens of Bettongia 2)enicillata become slightly larger than 

 the latter in other -specimens of B. j^enicillata, in B. Gaimardi, and in B. Lesueuri, and 

 considerablv larger in ^Bpypryumus. Tlie third teeth from, being smaller than the 

 second in Sypsiprymnodon and Bettongia become larger in Mpypryninus. The changes 

 ia size of the fourth molars are not serial : in B. penicillata and B. Lesueuri they are 

 of about the same size as in Hypsiprymnudon, and as the former are much larger 

 animals they appear out of proportion to the remaining teetli. In B. Gaimardi and 

 in j£pyprymnus they are of about the same relative size as in Mypsiprymnodon. 



The changes just described, namely, the reversal of the relative proportions of the 

 molars, are of considerable significance, in that they represent a necessary feature of the 

 herbivorous evolution, since they are indicated not only in the present group but also 



