. The Deseado formation of Patagonia . Ameghino and of which we found no insert a reproduction of the side view of the skull, andthe dentition is shown in fig. 24 a, and fig. 25 a. Thedental formula is -77^3^- Incisor i is a little larger thanthe other incisors. Each upper molar has a vertical groovenear the anterior external margin. In each upper premolar(after the first) and molar, there is a central pit surrounded 62 THE DESEADO FORMATION OF PATAGONIA by enamel, which is opposite the internal inflexion, andin a young individual, is presumably connected with thefold. In the same
. The Deseado formation of Patagonia . Ameghino and of which we found no insert a reproduction of the side view of the skull, andthe dentition is shown in fig. 24 a, and fig. 25 a. Thedental formula is -77^3^- Incisor i is a little larger thanthe other incisors. Each upper molar has a vertical groovenear the anterior external margin. In each upper premolar(after the first) and molar, there is a central pit surrounded 62 THE DESEADO FORMATION OF PATAGONIA by enamel, which is opposite the internal inflexion, andin a young individual, is presumably connected with thefold. In the same way, the last three lower premolars andthe lower molars each have an internal pit, adjacent tothe external inflexion. With advanced age all the teethshow closed roots, another primitive feature. In spiteof the closed roots, the full dentition, and the enamel onthe incisor; and on account of the deep inflexions and theisolated pits, I consider this genus a specialized side line,retaining many primitive features, and expect to find the. Fig. 27. Archaeohyrax patagonicus, after Ameghino—natural size. ancestor of the typotheres in some one of the related Casa-mayor genera. Ameghino described three species, A. patagonicus, whichwe have figured, and which has a length of 84 mm. frominc. I to m. 3 in both the upper and lower dentitions; , of the same size, but with the dental seriesclosed; and A. concentricus of larger size, the three lowermolars having a length of 38 mm. Plagiarthrus Ameghino Plagiarthnis Amcgh., 1897, Bol. Inst. Gcog. Argen., t. 18, p. 436. This genus is known only by the lower premolars andmolars, which are permanently growing teeth, composedof two subcylindrical cylinders almost entirely separated PLAGIARTHRUS 63 by the external and internal folds which almost meet inthe median line. On the outside, each tooth is coated witha layer of cement. When better known it may prove thatthis genus, so specialized in the character of the teeth,does not belo
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