Length from inc. 1 to occipital condyles 720 mm. Length from front of premax. to nasal opening 225 mm. Length of boss on premaxilla 77 mm. Length of nasal opening at top 80 mm. Width of nasal opening at top 88 mm. Length from premax. to lambdoidal crest 540 mm. Width across zygomatic arches 350 mm. Width across frontal bones 90 mm. Transverse diameter of the snout 115 mm. [Illustration: Fig. 113. Base of the skull—⅕ natural size; _i.1_, incisor the right side grown over toward the center as its mate is wanting; _i.2_, incisor 2; _Pal._, palatinum; _Pt._, pterygoid.] The lower jaws were associated with the above skull, and are complete to behind the third molars on both sides. They are very short and heavy, especially in the anterior portion, the symphysis extending back to opposite the middle of the second molar. The height under molar 3 is 150 mm. See frontispiece. From the upper dentition, I give the measurements of my two chief specimens, together with those given by Ameghino for his type of _P. sorondoi_, and the figures given by Gaudry; from which may be seen the amount of variation which individuals may show. UPPER DENTITION SPECIMEN SPECIMEN AMEGHINO’S GAUDRY’S NO. 3207 NO. 3250 TYPE SPECIMEN Total length, inc. 1 to m. 3 530 mm. Inc. 1, length above alveolus 133 mm. Inc. 1, antero-posterior diam. 49 mm. Inc. 1, transverse diam. 37 mm. 42 mm. Inc. 2, length above alveolus 174 mm. Inc. 2, antero-posterior diam. 59 mm. 77 mm. 65 mm. Inc. 2, transverse diam. 40 mm. 52 mm. 41 mm. Premolar 2, length 45 mm. 52 mm. 48 mm. 40 mm. Premolar 2, width 36 mm. 40 mm. 30 mm. 29 mm. Premolar 3, length 46 mm. 49 mm. 48 mm. 40 mm. Premolar 3, width 57 mm. 57 mm. 46 mm. 48 mm. Premolar 4, length 47 mm. 51 mm. 46 mm. 43 mm. Premolar 4, width 63 mm. 64 mm. 58 mm. 57 mm. Molar 1, length 55 mm. 55 mm. 57 mm. 55 mm. Molar 1, width 68 mm. 69 mm. 61 mm. 61 mm. Molar 2, length 68 mm. 77 mm. 70 mm. 57 mm. Molar 2, width 85 mm. 93 mm. 75 mm. 68 mm. Molar 3, length 75 mm. 68 mm. 83 mm. 64 mm. Molar 3, width 86 mm. 87 mm. 82 mm. 88 mm.