The type is specimen No. 3020, a fragmentary mandible with premolars 3 and 4 and molar 1 in place. Pm. 3 is two-rooted, but so small as to be entirely overshadowed by the succeeding pm. 4, hardly reaching a half the height of that tooth. On the last premolar and the first molar, the cusps are arranged in a trigonid in front and a talonid behind, the cusps being joined by thick ridges, making two connecting crescents. [Illustration: Fig. 147. Left mandible with premolar 3 to molar 2—4 times natural size.] [Illustration: Fig. 148. Left mandible internal side—4 times natural size.] MEASUREMENTS, SPECIMEN 3020 Lower dentition, premolar 3, length 1 mm. Lower dentition, premolar 4, length 5 mm., width 2 mm. Lower dentition, molar 1, length 4 mm., width 2 mm. Lower dentition, height under pm. 4 6.5 mm. Caenolestinae The subfamily is distinguished by the formula 4 1 4 3 -------, 4 1 3 3 pm. 4 not being enlarged, and the lower molars being turberculo-sectorial. In the Deseado formation this group is only represented by a single species, based on a single tooth found by Ameghino. =Pseudhalmarhiphus guaraniticus= Ameghino P. guaraniticus Amegh., 1903, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 2, p. 83. Based on a single tooth, similar to those found in the Santa Cruz. Abderitinae The subfamily is distinguished by the formula ? ? ? ? -------, 4 1 2 3 the fourth premolar being enlarged into a sectorial tooth on the sides of which are vertical striae. The molars are buno-lophodont. The Deseado has yielded only a tiny form, designated _Parabderites_, which differs from the Santa Cruz genus _Abderites_ in pm. 4, the same shape, but with few to no striae on its sides. =Parabderites minusculus= Ameghino P. minusculus Amegh., 1902, Bol. Acad. Nac. Cienc. Cordoba, t. 17, p. 43. The species as described by Ameghino is based on a lower jaw with pm. 3 to m. 3. The specific character is the lack of striae on pm. 4. No figure is given but the following measurements indicate the size. Lower dentition, premolar 3 to molar 3 9 mm. Lower dentition, height of mandible under pm. 4 4 mm. CHAPTER XVI BIRDS In the Deseado beds, birds occur in small numbers, Ameghino having described four species. The remains are generally found as isolated bones, and it is hard to associate the separate finds one with another. Beside this there are very few birds of the early Tertiary so known, as to make separate bones indicate the family or generic relationships. In the overlying Patagonian beds, a considerable number of species have been found, mostly of penguin-like birds, the various genera and species being based on the tarso-metatarsus. On the upper surface of the Deseado, we found several bones of this penguin-like type, but in all cases they were washed out, so that I have considered them as having come from the Patagonian.