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Show 1877.] PROF. OWEN ON A NEW SPECIES OF STHENURUS. 357 in which, as is well known, the true molars (a backward continuation 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 mammals1. 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 Coleman2. Such are the grounds which oppose my acceptance of the conclusions of a fellow labourer whose opinion I value. Prof. Garrod expresses them as follows :- " A n inspection of the plates in Prof. Owen's paper on these new genera (Phil. Trans. 1875, p. 245) makes it evident that they are scarcely 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 seq., under the names Protemnodon and Sthenurus. Professor Garrod assigns no grounds for their necessary inclusion in the section cited ; if he should be disposed to define them they will receive m y clue attention. In such inquiries and comparisons I would venture to express the advantage I have derived from definite conclusions as to the homologies 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. S. 1875, p. 52) relative to the position of the masseteric process, 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. S. 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. Comparing 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 m 3 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 (Hypsiprymninse) 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. 2 a) 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. Eartholomew's-Hospital Reports, vol. xii. p. \)2. |