44 Leontinia gaudryi Browse Brush 15% 44 LEONTINIDAE plains 2 Proadinotherium leptognathus Grass or Plains 2 Coresodon scalpridens Browse 1% 4 NESODONTIDAE 7 Asmodeus osborni Browse ? 2% 7 HOMOLADONTIDAE 6 Parastrapotherium holmbergi Browse ? 2% 6 ASTRAPOTHERIDAE 11 Pyrotherium sorondoi Browse ? 4% 11 PYROTHERIA 55 Cephalomys arcidens 22 Cephalomys plexus 19 Cephalomys prorsus Hard Open vegetation country 3 Asteromys prospicuus 1 Scotamys antiquus 1 Eosteiromys medianus 1 Litodontomys chubutensis 35% 102 RODENTS 9 Proeutatus lageniformis 1 Prozaedius planus Insects Open and leaves country 2 Prozaedius depressus 3 Proeuphractus setiger 2 Peltephilus undulatus 1 Palaeopeltis inornatus 5 Indeterminate 8% 23 EDENTATA 1 Plichenia lucina 1 Epanorthus chubutensis 5 Callomenus praecursor Insects ? and flesh 2 Pharsophorus tenax 1 Pharsophorus mitis 3% 10 MARSUPILAIA 3% 11 BIRDS Open country 100% 293 In our collection, all from one point, there are thirty-nine different species. Beside these Ameghino has described a considerable number of species, some of which in time will probably turn up at our locality; but others and I think the majority will be found to be representative of other localities which he worked. It is to be expected that a difference of locality will make a little difference in the fauna. Further I expect that no two localities represent exactly the same period of time, though they may do so approximately; but some of these local deposits must have been begun earlier, and others probably lasted to a later period. Thirty-nine species of mammals and land birds is a fairly varied fauna for one spot; and the time element involved in laying down the 50 feet which separated the bottom from the top of the Deseado deposit is not probably very long; for the material of which the deposit is composed is of a character which would have been laid down fairly rapidly.