As to the age of the Deseado deposit which we worked. It is under the Patagonian, and therefore must be as old as the Oligocene. On the other hand it must be as young as the Eocene, lying as it does above the Upper Cretaceous. Of the three general faunas described it is clearly more advanced than either the Casamayor, or the Astraponotus; so should be put as the youngest of these three. The Colpodon, the Astrapothericulus and the Notohippus, faunas are said to be interstratified with the Patagonian and therefore of the same age. The amount of advancement from the Casamayor to the Deseado is considerable and the relationships of the Deseado are fairly close with the various genera of the Santa Cruz; so that I should put the Deseado as far up as possible toward the Santa Cruz. The Santa Cruz is above the Patagonian, and I think that the Deseado should be put just before the Patagonian; that is in the Oligocene, but just what part of the Oligocene can only be determined when the other faunas have been further studied. CHAPTER III THE DESEADO FAUNA The exposure of the Deseado, which the Amherst party worked, yielded 293 specimens, each presumably representing an individual. (There were besides these a few that were indeterminate and are not therefore included.) The consideration of the fauna as a whole suggests certain ideas as to the country in which the animals lived, and also certain comparisons with the fauna of the preceding and later faunas. The first striking feature is the presence of so many excessively large animals, as _Asmodeus_, _Parastrapotherium_, and _Pyrotherium_, in each case forms larger than a rhinoceros. Further than that they are in each case the largest members of their family, even larger than the representatives in the later Santa Cruz. This would indicate a period in which living conditions were at a high grade, suggesting both abundance of food and a moderate climate. The following table will give a good idea as to the range of species, and their relative abundance in the fauna, also a suggestion as to the class of food they used; and from that an idea as to what sort of country they occupied: PER NUMBER SPECIES FOOD COUNTRY CENT 3 Hegetotherium shumwayi 7 Prosotherium garzoni 17 Prosotherium triangulidens 1 Eutrachytherus grandis 4 Eutrachytherus spegazzinius Grass, bark Plains and browse 1 Isoproedrium solitarium 2 Phanophilus dorsatus 4 Argyrohyrax proavus 1 Plagiarthrus clivus 14% 40 TYPOTHERIA 1 Protheosodon coniferus Grass Plains 15 Notodiaphorus crassus 6% 16 LITOPTERNA 19 Rhynchippus equinus Grass Plains 7% 19 RHYNCHIPPIDAE