As the Australian Continent, the great me tropolis of the Marsupial quadrupeds, still remains but very partially explored, and as new species and even genera of Marsupials continue at each expedition to reward the re searches of the scientific traveller; and as, more over, the recovery of two lost but distinct from the ruins of a former world makes it reasonable to suppose that other types of Marsupials remain still hidden in the crust of the earth, it can hardly be expected that the zoologist should be able to arrange in a natural series, with easy transitions according to the order of their affinities, the few and diversified forms of this implacental group which are at present known.
In the subjoined classification the modifica tions of the digestive system have been taken as the guide to the formation of the primary groups of the Marsupialia.
The Continent, however, in which the Mar supials exist in greatest number and variety, is characterized by the paucity of organized matter upon its surface, and consequently few of the species are nourished by a well-defined diet. I\ o large carnivorous quadruped could without much difficulty have found subsistence in the wilds of Australia, prior to the intro duction of civilised man and his attendant herds; and we find, in fact, that the native genera which are the most decidedly carnivo rous do not include species larger than the dog. \Ve can only reckon among these strictly car nivorous species the Thylacines and the Da syures ; and, on the other hand, not more than two or three Marsupial genera feed exclusively on vegetable substances. The remainder de rive a promiscuous nutriment from dead or decaying animal and vegetable matter, crus tacea, and the refuse of the sea-shore, insects in their perfect and larva states, live birds, young and succulent sprouts, leaves, fruits, tke. The terms, therefore, which will be given to the different primary subdivisions in the present classification of the Marsupialia must not be understood to indicate strictly or ex clusively the nature of the food of the species severally included in these groups, but rather their general tendency to select for their support the substances implied by those designations.
The incisors are of equal length and regu larly arranged in the segment of a circle with an interspace in the middle of the series of both jaws. The external incisor on each side is the strongest. The laniary or canine teeth
are long, strong, curved, and pointed, like those of the dog tribe. The spurious molars in this as in all other Marsupials have two roots; their crown presents a simple com pressed conical form, with a posterior tubercle which is most developed on the hindmost. The true molars in the upper jaw are unequally triangular, the last being much smaller than the rest; the exterior part of the crown is raised into one large pointed middle cusp and two lateral smaller cusps obscurely developed ; a small strong obtuse cusp projects from the inner side of the crown. The molars of the lower jaw are compressed, tricuspidate, the middle cusp being the longest, especially in the two last molars, which resemble closely the sectorial teeth (dents carnassars) of the dog and cat.
The fore feet are 5-digitate, the hind feet 4-digitate. On the fore foot the middle digit is the longest, the internal one or pollex the shortest; but the difference is slight. On the hind foot the two middle toes are of nearly equal length and longer than the two lateral toes, which are equal. All the toes are armed with strong, blunt, and almost straight claws.
The only known species of this genus,—the Thylaciue ( Thylacinus Harrisii, Temm., Di delphys Cynocephalus, IIarris,) is a native of Van Dieman's Land, and is called by the Colonists the " Ilyana." It is the largest of the carnivorous Marsupials, equalling in size the shepherd's dog, but is of a broader build, and stands lower on its legs. Its head is of disproportionate magnitude. The principal characteristic of its colour is the transverse black bands which traverse the back. It dwells in caverns and holes in the rocks, and seeks its prey by night, devouring the smaller native quadrupeds, and at the present day committing destructive ravages on the numerous flocks of sheep which have been introduced by the Euro pean settlers into the island. Even the spines of the Echidna seem to be no defence against the destruc tive and voracious propensities of the powerful Thy lacine, for the partly digested remains of one of these monotremes have been found in its stomach.
In confinement the Thvlacine titters from time to time a short guttural cry, and appears in the day time exceedingly inactive and stu pid, presenting an almost continual movement of the nictitating mem brane of the eye.