In addition to the above, Ameghino simply gives the following measurements: First upper tooth, ant.-post. diam. 20 mm., trans. diam. 13 mm., height 80 mm. First lower tooth, ant.-post. diam. 21 mm., trans. diam. 16 mm., height 80 mm. Last lower tooth, ant.-post. diam. 28 mm., trans. diam. of ant. lobe 18 mm. Last lower tooth, trans. diam. of post. lobe 16 mm., median diam. 7 mm. [Illustration: Fig. 136. _A_, lower molar, side view—natural size; _B_, lower molar, cross section—natural size; _C_, upper molar, cross section—natural size, after Ameghino.] =Octodontotherium crassidens= Ameghino O. crassidens Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 505. This second species is based on isolated teeth of larger size than the preceding, with measurements as follows: Upper molar, ant.-post. diam. 26 mm., trans. diam. 18 mm. Lower molar, ant.-post. diam. 26 mm., trans. diam. of ant. lobe 21 mm., trans. diam. of post. lobe 16 mm. =Orphodon= Ameghino Orphodon Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 658. Orphodon Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 504. The teeth of this type are a mass of dentine, each surrounded by a thin layer of cement, and each tooth subcylindrical in section, with the crown worn to two apposed oblique planes. The genus resembles _Ortotherium_. [Illustration: Fig. 137. Type—natural size, after Ameghino.] =Orphodon hapaloides= Ameghino O. hapaloides Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 658. O. hapaloides Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 505. In addition to the above, Ameghino gives a figure, here reproduced, and the following measurements: Tooth, greatest diam. 12 mm., lesser diam., 10 mm. CHAPTER XV MARSUPIALIA In our collection, the marsupials are represented, unfortunately, by but a few specimens; though this Deseado fauna included, as is shown by the fragmentary remains, a wide range of forms from _Pilchenia_, the size of a mouse, up to the bear-sized _Proborhyaena_. The small forms were probably insectivorous, while the larger forms took the place of the carnivores, the absence of true _Carnivora_ being one of the striking features of the fauna of South America during earlier Tertiary times.