Ameghino briefly describes, without a figure, a species in which premolar 4 and molar 3 together measure 14 mm. I have assigned to this two specimens, the one with pm. 2 incomplete, pm. 3 complete, and m. 2 also complete. These teeth measure the same as Ameghino’s and I think are the same. There is also a fragment of the upper jaw with molars 2 and 3, though imperfect. From these it appears that we have to do with an animal not only smaller than the preceding, but on much slenderer lines. The following are the measurements of the two specimens. SPECIMEN 3117 Upper dentition, molar 2, length 8 mm., width 6 mm. Upper dentition, molar 3, length 2 mm., width 6 mm. SPECIMEN 3060 Lower dentition, premolar 3, length 6 mm., width 2.5 mm. Lower dentition, molar 2, length 7 mm., width 4 mm. [Illustration: Fig. 143. Left mandible—natural size.] =Notogale tenuis= Ameghino ? Pharsophorus tenuis Amegh., 1897, Bol. Inst. Geog., Argen., t. 18, p. 504. This species was founded by Ameghino on a single lower premolar 3 which is 3 mm. in length. No further description is given and no figure. =Proborhyaena= Ameghino Proborhyaena Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 501. The genus is founded on a large lower jaw carrying the canine and premolars 3 and 4 and roots or alveoli for the other teeth. It is the largest carnivore recorded from Patagonia, and as large as a small bear. It is not possible to place its exact relationships, for the most essential teeth are wanting, but it is certainly a distinct genus as indicated by the reduced size of premolar 4 and the plump character of the teeth. =Proborhyaena gigantea= Ameghino P. gigantea Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 501. We found no specimens of this great carnivore, so I am reproducing Ameghino’s figure and measurements. The heavy canine is channeled on the sides and much worn on the posterior face. Premolar 3 is a plump tooth, its crown consisting mostly of a single median cusp, but with a small heel behind, and, strikingly enough, premolar 4 is a smaller and simpler tooth with a single cusp. [Illustration: Fig. 144. Right mandible—½ natural size, after Ameghino.] MEASUREMENTS Lower dentition, canine, antero-posterior diameter 30 mm. Lower dentition, canine, transverse diameter 20 mm. Lower dentition, premolar 1 to molar 3 145 mm. Lower dentition, height of mandible under pm. 4 60 mm. =Proborhyaena antiqua= Ameghino ? Borhyaena antiqua Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 655. Proborhyaena antiqua Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 502.