We pass on to the other curious order of non-placental mammals, that of the Monotremata, so called from the structure of their organs of evacuation with a single orifice, as in birds.
Further, it is considered that too much weight has been assigned to the characters distinguishing monotremes from other mammals, foetal marsupials showing a monotreme type of coracoid, while it is probable that in the long run it will be found impossible to maintain the essential dissimilarity between the milk-glands of monotremes and other mammals.
Douglas Ogilby (Catalogue of Australian Mammals, p. 1, Sydney, 1902), but expressed the hope "that further inquiries might be made by naturalists in Australia as to the actual finding of such eggs in the burrows, so that this most interesting point might be finally settled."
The comparatively few indigenous placental mammals, besides the dingo or wild dog - which, however, may have come from the islands north of this continent - are of the bat tribe and of the rodent or rat tribe.
The same deposits have yielded remains of small mammals whose dentition approximates more nearly to that of either polyprotodont marsupials or insectivores; and these may be conveniently noticed here without prejudice to their true affinities.