Passing on to another point, it has to be noticed that exception has also been taken to Flower’s view that the replacing tooth of marsupials and its deciduous predecessor correspond to the fourth, or last premolar of placentals. The question has been discussed in considerable detail in the Zoological Society’s _Proceedings_ for 1899 by the present writer, who had for material the dentition of certain extinct South American mammals quite unknown to science at the time Flower’s paper was written. The result of these comparisons was to render it evident, in the present writer’s opinion, that the replacing tooth of the marsupials corresponds to the third, instead of to the fourth, premolar of placentals. From this it follows that marsupials agree with placentals in possessing only three pairs of true molars; the first of the four teeth in the former behind the replacing tooth being the last milk-premolar (which is never replaced) instead of, as supposed by Flower, the first true molar. This conclusion, as pointed out by the present writer in the paper referred to above, had really been arrived at years previously by Owen, who also believed the replacing tooth to correspond to the third premolar of placentals. In thus bringing marsupials into line with placentals as regards their dentition, this later interpretation accords well with recent discoveries in regard to other parts of the organisation of the former animals. It should, however, be mentioned that the newer view is by no means accepted by all zoologists, although it has received the support of the well-known American paleontologist, Dr. J. L. Wortman,[7] who is specially qualified to form a trustworthy opinion on a point of this nature. Finally, whatever be the eventual verdict as to the serial homology of the marsupial dentition as a whole, and also as to that of the replacing premolar, Flower must always be credited with the discovery that marsupials replace only a single pair of teeth in each jaw by vertical successors. The other papers on dentition referred to above as having been written by Flower about the same time are, although interesting in their way, of far less importance than the one published in the _Philosophical Transactions_. Indeed the one read before the British Association in 1868 and published in the _Journal of Anatomy and Physiology_ for the same year, is little more than a recapitulation of the results arrived at in the former.