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Show 194 MR. W. A. FORBES ON THE KOALA. [Jan. 18, ordinary caecum (see the description and figure by Prof. Flower, Med. Times and Gazette, Dec. 14, 1872, p. 642). In its teeth being all rootless, as well as in the equality in the number of its incisors, Phascolomys differs from all other Marsupials. But it is highly probable that this peculiar Rodent-like dentition has been brought about in accordance with its mode of life, and that therefore these features, being adaptive, have in reality less importance in classification than has been assigned to them. Moreover, in a very young Wombat's skull preserved in the Hunterian Museum (1795 D ) , in which the first three molar teeth only in each jaw have cut the gum and are quite unworn, each lobe of the teeth has two quite distinct, though small cusps; hence the second and third teeth on each side have four distinct cusps, and the anterior two, as in the Phalangers generally. The caecum is no doubt peculiar, and quite unique amongst Mammalia, any resemblance to the " appendix vermi-formis" of the highest Primates being fanciful. If in these points sufficient reason is considered present for elevating the Wombats to the position of a primary group of the Marsupials-whether such group be called a tribe or a family is no matter-it should not be forgotten that in some features Phascolarctos, too, is nearly as peculiar as Phascolomys itself. .These are mainly :-the peculiar alisphe-noidal bulla of the skull; the extraordinary complicated liver, with the elongated gall-bladder; the immensely developed caecum and caecum-like ascending colon, with their longitudinal folds of mucous membrane ; and the absence of an azygos lobe to the lungs, the Wombats agreeing with the Phalangers in possessing one. Hence it appears to me to be a more natural course to keep these three groups together as subdivisions of a larger one, though whether that one be called a family, or made into a larger section, will depend on the value attached to those ideas by different naturalists. Adopting the former as most convenient, they might be defined briefly as follows :- PHALANGISTIDAE. Diprotodout Marsupialia, with clavicles, and not more than six incisors above. The hallux present; the 2nd and 3rd digits of the pes smaller than the others, and more or less united together by integument. Stomach not sacculated. Caecum present. Glaus penis more or less bilobed ; vaginae provided with median culs-de-sac which may unite. 1. PHALANGISTIN^E. Teeth rooted; superior incisors 3.3; at least one small additional premolar on each side above. Tail well developed. No cheek-pouches. Stomach and ascending colon simple. Caecum long, simple. Liver not complicated by secondary sulci, and with distinct caudate and Spigelian lobes. Lungs with an azygos lobe. Vaginal culs-de-sac coalesced (at least in Phalangista). Phalangista, Cuscus, Relideus\ Acrobata\ Dromicia1. l For an opportunity of dissecting examples of these genera I a m indebted to the liberality of our President. |