For the lower dentition, I give the figures which Ameghino records for his _P. sorondoi_, those given by Gaudry for his _P. romeri_, and the measurements of specimen No. 3207. The tushes in the lower jaw I would designate as incisors 2; because when the jaws are closed these diverge and their tips bite against the tips of the upper incisors 2. The first incisor seems to have been gradually lost and no space left for it in the front of the mandible, just as it was reduced and lost in the development from _Moeritherium_ to _Polymastodon_ or equivalent types. [Illustration: Fig. 114. Lower dentition—⅕ natural size; edges of teeth broken off in my specimen are indicated in outline.] LOWER DENTITION SPECIMEN AMEGHINO’S GAUDRY’S NO. 3207 TYPE SPECIMEN Incisor 2 to molar 3, length 510 mm. 540 mm.‡ 415 mm.‡ Premolar 2 to molar 3, length 325 mm. 280 mm. 272 mm. Inc. 2, length above alveolus 133 mm. 188 mm.‡ 168 mm.‡ Inc. 2, antero-posterior diam. 55 mm. 60 mm. 66 mm. Inc. 2, transverse diam. 40 mm. 36 mm. 44 mm. Premolar 3, length 46 mm. 50 mm. 54 mm. Premolar 3, width 36 mm. 31 mm. 35 mm. Premolar 4, length 55 mm. 45 mm. 50 mm. Premolar 4, width 46 mm. 45 mm. 47 mm. Molar 1, length 65 mm. 50 mm. 51 mm. Molar 1, width 59 mm. 52 mm. 54 mm. Molar 2, length 73 mm. 56 mm. 66 mm. Molar 2, width 73 mm. 63 mm. 66 mm. Molar 3, length 69 mm. 67 mm. 71 mm. Molar 3, width 74 mm. 66 mm. 69 mm. ‡ Figures taken from illustrations. Four cervical vertebrae were preserved with the skull number 3207, of which only about a third of the atlas is represented, but fortunately we found a complete atlas isolated and of the same size. The measurements for the atlas are taken from this separate specimen. While my skull, especially the teeth, seems to have been larger than the skull Gaudry described, the cervicals are a little smaller. I give the measurements of the cervicals which we found, comparing them with the figures given by Gaudry. SPECIMEN GAUDRY’S 3344 SPECIMENS Atlas, antero-posterior length 120 mm. 140 mm. (without hypophysis) Atlas, greatest width 304 mm. 365 mm. Atlas, height 129 mm. 140 mm.