258 NATURAL SCIENCE [October 
a condor, of whose size we may form an idea from the head, which 
is much larger than that of a horse. Being great runners, they 
gave chase to the mammals of that epoch, even to the most gigantic 
of them, and were doubtless not afraid to measure their strength 
with the Dinosaurs themselves. 
But the animals of that period which in our formations offer 
special interest are the mammals. While in Europe and North 
America only some small representatives of that class lived, insig- 
nificant and little specialised, in Argentina they had attained an 
extraordinary development ; they were large and small, of the most 
varied forms, showing that the Cretaceous deposits of our country 
contain the ancestors of almost all the groups of mammals which 
have succeeded each other one by one in different regions of the 
earth. 
It would be a lengthy task to give you an account of the 
mammalian fauna of that time; it is only possible for me to outline 
the subject and to limit myself to noticing some forms related to 
others with which you are familiar. 
That which first attracts the attention of the naturalist in this 
fauna is the presence of remains of the Primates or inferior quad- 
rumana (Notopithecidae) of a greatly reduced size, which appear 
to be the ancestors of the extinct lemurs of Europe and North 
America, and of those existing in the South of Asia and Africa, 
while another branch leads to the Homunculidae (Homunculus, 
Anthropops, Pitheculus, ete.) of the Tertiary of our own country, 
which are the ancestors of the monkeys of — worlds, and conse- 
quently of man. 
The carnivorous mammals were represented solely by a group 
to which I have given the name Sparassodonta, whose size varied from 
that of a ‘laucha’ (Pharsophorus) to that of the largest bear (Probor- 
hyaena); they exhibit a mixture of the characters of placentals and 
marsupials, and represent the stock whence were derived the car- 
nivorous marsupials of the Australian continent, the placental 
carnivores of both hemispheres, and a large number of the extinet 
forms of the northern hemisphere designated under the name 
of Creodonts. 
Another most interesting group is that of the Plagiaulacoidea 
(Polydolopidae, Abderitidae, Epanorthidae, ete.), arma marsupial 
mammals with a dentition of the type of the Australian kangaroos, 
but with the limbs more nearly equal, with five digits on each foot, 
and with traces of syndactylism. They were extremely numerous, 
and gave origin to the greater portion of the marsupials of Australia, 
designated under the name of Diprotodonts, a group of which the 
1 These fossils may now be seen in the Department of Geology in the British Museum 
(Natural History).—Trans, 
