1877.] PROF. OWEN ON A NEW SPECIES OF STHENURUS. 357 
in which, as is well known, the true molars (a backward continua- 
tion of the deciduous series) are always on the move in a curve from 
behind forward, and are shed in front as they are developed behind. 
The sockets or cases of the huge complex grinders are more distinct, 
as such, from the surrounding maxillary or mandibular bones, than 
in other mammals’. This dynamic has been well exemplified as 
efficient in the vertical movements of permanent incisors and canines 
of the human subject by the present Lecturer on Dental Surgery at 
St. Bartholomew’s Hospital, Mr. Alfred Coleman?. 
Such are the grounds which oppose my acceptance of the conelu- 
sions of a fellow labourer whose opinion I value. Prof. Garrod ex- 
presses them as follows :— 
** An inspection of the plates in Prof. Owen’s paper on these new 
genera (Phil. Trans. 1875, p. 245) makes it evident that they are 
searcely distinguishable from Dendrolagus, and must be included in 
the Dorcopsis section of the family.” 
The genera alluded to are those defined in the Philosophical 
Transactions, 1874, p. 245 et seg., under the names Protemnodon 
and Sthenurus. 
Professor Garrod assigns no grounds for their necessary in- 
clusion in the section cited ; if he should be disposed to define them 
they will receive my due attention. 
In such inquiries and comparisons I would venture to express the 
advantage I have derived from definite conclusions as to the homo- 
logies of the teeth, resulting in a power of defining them individually by 
symbols; for whether such symbols be accepted or not, they briefly 
but unmistakeably show the writer’s meaning. In the quotation 
(P. Z. 8. 1875, p. 52) relative to the position of the masseteric pro- 
cess, one could not be sure which molar Prof. Garrod meant without 
referring to the plate vii. And again, in the description of his plate ix. 
(P. Z. 8. 1875), the author writes :—‘‘ the third and fourth rows the 
upper and lower third left molar” (p. 59). Counting the molars 
from before backwards the third would be the penultimate one. 
Coniparing the figures with the original specimen now in the British 
Museum I find fig. 3 most resembling, in the relative size of the 
hinder lobe, the last of the molar series, viz. the fourth, counting 
backward; but this is the homologue, in my view, of the third true 
molar in the typical diphyodont dentition, consequently bearing the 
symbol m3 in Plate XXXVIII. figs. 8, 15, of the present paper. 
But if the molar tooth, fig. 3 in Prof. Garrod’s plate, be the 
homologue of figs. 8 and 15 in mine, it yields a comparison bearing 
on the question at issue. In many Wallabies, as in the Potoroos 
(Hypsiprymnine) the last molar, m 3, differs from that in Macropus 
proper and in Sthenurus by its smaller relative size, especially of 
its hinder lobe; and I see in this character of Dorcopsis, associated as 
1 «The bony plate (ib. fig. 2a) forming the sockets of the growing teeth is 
more than usually distinct from the body of the maxillary, and participates in 
this revolving course, advancing forwards with the teeth.” (*Odontography,’ 
1840-45, p. 639.) 
2 St. Bartholomew’s-Iospital Reports, vol. xii. p. 92. 
