458 Prof. K. A. von Zittel—On the Mammalia. 
group of animals which the investigations of Ameghino has brought 
to light in Patagonia is new and altogether peculiar, and in it are to 
be found the ancestors of the Hdentates, Rodents and Apes of the 
present neotropical kingdom. 
There are great difficulties in the way of precisely determining 
the age of a fauna thus new and circumscribed, more particularly 
since the geological relations do not yield any definite information. 
The Santa Cruz beds rest directly on the “‘Guaranian formation,” the 
lower portion of which consists of marine deposits, undoubtedly 
belonging to the Cretaceous; whilst the upper consists of con- 
glomerates and coarse sandstones, in which the remains of Opistho- 
coelous Crocodiles and Dinosaurs (?) and the imperfectly preserved 
mammalian fragments mentioned above (Macropristis, Pyrrhotherium, 
etc.) have been discovered. The Santa Cruz formation is overlaid 
by flows of Basalt, and it forms the foundation for the marine 
deposits with Ostrea Patagonica, Pecten Paranensis, and a great 
number of other fossil shells which have been already examined by 
D’Orbigny, Darwin and Bravard, and determined to be Tertiary. 
Darwin held the marine deposits to be Eocene, D’Orbigny, Miocene, 
and Ameghino, Oligocene. Direct points of comparison with North 
American or HKuropean Tertiary strata are here also wanting, so that 
the age of the Santa Cruz and Patagonian formations must be wholly 
determined from the general character of the fossil remains. 
Ameghino places the mammalian fauna of Santa Cruz in the 
Hocene. That, however, the existence of Amblypoda, Tillodontia, 
Creodontia, and Plagiaulacide cannot be advanced in favour of this 
view, has already been mentioned. Amongst the Marsupials, forms 
of a distinctly ancient stamp are wanting, and in particular one fails 
to find close ties to the Mesozoic Polyprotodontidee and Allotheria. 
Amongst the Perissodactyla, the Macrauchenide stand on a primitive 
rank as regards their dentition and the structure of their extremities, 
when compared with their later successors in the Pampas formation ; 
on the other hand the Proterotheride, which, as regards their den- 
tition, may be the most readily compared with the Anoplotheridz 
and Palzotheride, have far outran these latter in the reduction of 
the lateral metapodials and in the complete differentiation of the 
extremities. ‘The remarkably numerous and varied Hdentates do 
not in the least correspond with the ideas which one is justified in 
holding respecting the ancestors of this order. They remain, indeed, 
in size far behind the giant forms of the Pampas formation, but they 
are already just as distinctly divided into sub-orders (Vermilinguia, 
Tardigrada, Gravigrada, Glyptodontia and Dasypoda) as in the 
Pleistocene, and they stand in all the important features of the 
dentition and build of the skeleton, on a high grade of differentia- 
tion. ‘The molars are already of a prismatic form, incisor teeth are 
only known in two genera, and a change of teeth appears to have 
taken place just as seldom as in the majority of living Hdentates. 
Skull and skeleton do not materially differ from those of younger 
genera, and the characteristic dermal shields of the Glyptodonts and 
Dasypoda from the Santa Cruz formation are in reality built up like 
