360 PROF. OWEN ON A NEW SPECIES OF STHENURUS. [Apr. 17, 
larger than the existing kinds, manifest in a highly interesting and 
suggestive way an approximation to the Notothere and Diprotodous. 
In Nototherium, although the premolar (by position) is charac- 
terized by an outer and an inner plate, antero-posteriorly disposed’; 
yet the transverse breadth of the tooth is proportionally so much 
greater than the fore-and-aft length, and the connecting ridges of 
the two plates, through the folding of the inner one, are so large, 
that the hind part of the premolar already assumes the character of 
a lobe of the transversely ridged dilophodont molars, In Diprotodon 
the dilophodont character is better shown’, and the premolar (by 
position) is the first of the series of such molars, differing only in its 
inferiority of size. The qualification ‘“‘by position’’ means that the 
tooth is not a veritable premolar, it never displaced vertically a de- 
ciduous predecessor, either in Nototherium or Diprotodon, but is the 
homologue of d3 in the Pig and Kangaroo. 
Macropus, Sthenurus, Procoptodon exemplify stages of transition 
to the exclusively vegetarian character of the molar series exemplified 
by Diprotodon. The genera Halmaturus, Dorcopsis, Dendrolagus, 
Hypsiprymnus exemplify as many stages in the modification of the 
teeth for a mixed diet, which, in the Diprotodont series of Marsu- 
pialia, culminated carnivorously in Thylacoleo. Here the upper 
anterior incisors, 71, acquired their largest proportional size with the 
change of the trenchant for the piercing or laniary type. The single 
lower pair of incisors underwent the same modifications. The con- 
versicn of the premolar, in size and shape, to a carnassial tooth, and 
the reduction of the molars in number and size to the tubercular 
condition of the feline molar, are exemplified, in Thylacoleo, with 
corresponding figures of the jaws and teeth of our Cave-Lion and 
Cave-Hyzeua, in plate vi. of my ‘ Researches on the Fossil Mammals 
of Australia.” In this work a preliminary chapter is devoted to the 
extinct Marsupials of England, in which it is shown that, at the 
oolitic period, our Marsupials had also diverged, by modifications of 
the fundamental type, into species exemplifying the ‘ polyprotodont’ ® 
and the ‘diprotodont’* suborders— and that, in the formal or 
adaptive characters of the teeth, species diverged from the common 
carnivorous or insectivorous types exemplified in Stylodon’ and 
Thylacotherium’, to the vegetarian type in Bolodon’ and Stereogna- 
thus* in one direction, and to the carnivorous type exemplified by 
Triconodon and Plagiaulaz,.in the opposite route. 
EXPLANATION OF THE PLATES. 
Pratt XXXVII. 
Sthenurus minor, Ow. 
Fig. 1. Palatal surface of skull with right and left molar series. 
2. Outer side view of alveolar part of the right maxillary, with the 
molar series iz situ, and the undeyeloped premolar exposed in its 
formative cell. 

1 © Researches,’ &e. vol. ii. pl. lxxxviii. figs. 11-16. 2 Thid. pl. exxiv. d 3. 
* [bid. pl. ii. fig. 17. 4 Tbid. pl. iv. fig. 16. 
5 [bid. pi. ii. fig. 14. 6 Jbid. pl. i. fig. 28. 
7 Tbid. pl. iii. fig. 5. 8 [hid. pl. iv figs, 9-15. 
