_Coenolestes_, a remarkable form recently described from America, belongs to the diprotodont section, and is the only living member of the section known outside the Australian region[153]. An exceptional dentition is seen in the case of the extinct _Thylacoleo_, in which the functional teeth are reduced to two pairs; one pair of large cutting incisors and one of compressed sharp-edged premolars. EDENTATA. Some Edentata, viz. the ant-eaters (Myrmecophagidae) are, as far as is known, absolutely toothless at all stages of their existence; being the only mammals except _Echidna_ in which no tooth germs have been discovered; others, viz. the Manidae, though showing foetal tooth germs, are quite toothless in post-foetal life; others, viz. some of the armadillos, have the largest number of teeth met with in land mammals. The teeth are homodont except in the Aard Varks, and grow from persistent pulps. In the sloths (Bradypodidae) and the Megatheriidae, there are five pairs of teeth in the upper and four in the lower jaw. The teeth of sloths consist of a central axis of vasodentine, surrounded firstly by a thin coating of hard dentine, and secondly by a thick coating of cement. In no living Edentate have the teeth any enamel; it has, however, been described as occurring in certain early Megatheroid forms from S. America[154], and an enamel organ has also been discovered in an embryo _Dasypus_[155]. In the Armadillos (Dasypodidae) the number of teeth varies from 8/8 or 7/7 in _Tatusia_, to upwards of 25/25 in _Priodon_, which therefore may have upwards of a hundred teeth, the largest number met with in any land mammal. In _Tatusia_ all the teeth except the last are preceded by two-rooted milk teeth. The Aard Varks are diphyodont, and milk teeth are also known in a species of _Dasypus_, but with these exceptions Edentates are, as far as is known, monophyodont. In _Glyptodon_ the teeth are almost divided into three lobes by two deep grooves on each side. The Aard Varks (Orycteropodidae) are quite exceptional as regards their teeth, which are cylindrical in shape, and are made up of a number of elongated denticles fused together. Each denticle contains a pulp cavity from which a number of minute tubes radiate outwards. These teeth are diphyodont and somewhat heterodont, eight to ten pairs occur in the upper jaw and eight in the lower, but they are not all in place at one time. The last three teeth in each jaw are not preceded by milk teeth[156]. SIRENIA. The teeth of Sirenia show several very distinct types, the least modified being that of the extinct Halitheriidae, which have large incisors in the upper jaw, and five or six pairs of tuberculated grinding teeth in each jaw, the anterior ones being preceded by milk teeth.