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Show 922 MR. R. LYDEKKER ON THE DENTAL FORMULA OF [Nov. 14 as this part of the skull is concerned, in deriving the Whalebone from the Toothed Whales. But whether such is the true phylo-geny may be left an open question ; and I may add that, for several reasons, 1 do not propose on this occasion to discuss the geological age of the deposits from which Prosqualodon was obtained. 6. The Dental Formula of the Marsupial and Placental Carnivora. By R. L Y D E K K E R. (Plate LXII.) [Received October 21, 1899.] Since the views expressed in the ' Study of Mammals'l with regard to the dental succession in the Mammalia generally, and the homology of the individual teeth of the cheek-series of the Marsupials with those of the Placentals, are out of harmony with the results of recent investigations, I ^think the time is ripe for a statement that I, as the surviving author of that work, no longer hold them. And I do this the more readily because it appears to me that some emendations in regard to the names employed for certain of the teeth of the cheek-series are urgently required. I may commence by the statement that I fully accept the view that the milk-teeth pjlus the so-called true molars constitute the first, or original series, and that the premolars form the second series ; this being precisely the opposite of the view taken in the work referred to2. Apart from other considerations, 1 regard the fact that the last tooth of the milk-molar series (as well as sometimes the tooth in advance of it) is always similar in structure to the true molars as a very strong argument in favour of this view. And I likewise accept the view that the whole of the teeth of modern Marsupials, with the exception of the single replacing pair in each jaw, belong to the first series. This being so, I come, without further preliminaries, to the consideration of the special subject of the present communication; that is to say, the serial homology of the individual cheek-teeth in the Marsupial and Placental Carnivora, and the dental formula that will best express this homology. It will simplify matters to confine our attention in the main to the teeth of the lower jaw, as what holds good for these will be likewise applicable in the case of those of the upper jaw. To go no further back than the publication of his ' Odontography,' we find Sir E. Owen in that work 3 giving the lower dental formula of Canis, which may be regarded as typical for the 1 Flower and Lydekker, 1891. 2 I do not propose to take into consideration the evidence in favour of the occasional presence of an aborted successional series to the true molars. * Page 475. |
