104 DEUXIÈME ASSEMBLÉE GÉNÉRALE 
theriidæ, probably of Perissodactyl affinities. The rhinoceroses have been 
traced back in the Lower Oligocene to animals (Trigomias) with several 
incisors as well as with canine teeth (OsBorx !, Lucas ?). 
The law of local adaptive radiation with its polyphyletie consequences 
has completely altered our conception of several Oligocene families, as 
follows. The Titanotheriidæ (OsBorx*) break up into four genera, which 
evolve independently from the base to thesummit of the Oligocene, namely, 
Titanotherium, Megacerops, Symborodon, and Brontotherium; divergence 
isindicated by dolichocephaly and brachycephaly as well as by other charac- 
ters (Fig. 7). Similarly the Equidæ break up into four and possibly five 
distinct contemporary phyla, and it now begins to appear probable that 
the line giving rise to Equus, separated off from the other horses as 
early as the Lower Oligocene (OsBorN, Ginzey: Fig. 4). The Oreodon- 
tidæ, represented by two phyla in the Upper Eocene, now present three 
phyla, namely, Agriochærus, Oreodon, Leptauchenia (Marrnew). Three 
phyla of Camelidæ are also recognized, namely, those represented by 
Paratylopus, Poëbrotherium, and Pseudolabis (Marraew Fig. 5). Simi- 
larly among the Felidæ, the Machærodont division, the only felines re- 
presented in America at this time, breaks up into the stout-limbed Æo- 
plophoneus series ancestral to Machærodus and Smilodon, the slender- 
limbed Dinictis*, and a third series represented by Nimravus (Fig. 6). 
Among the gaps in the Oligocene are the entire absence of Primates, 
the genera Laopithecus and Menotherium, formerly associated with the 
Primates, proving to be singularly primitive tritubercular Artiodactyls. 
An important problem is the actual relationships of the Artiodactyl genera 
Protoceras, Leptomeryx, Hypertragulus, and Hypisodus, which according 
to Scorr’s theory above alluded to, represent with the Oreodontidæ an 
independent radiation of American Artiodactyla wholly without affinity 
with the European Tragulines. 
Tue MiocEXE FAUNA. 
In our Miocene, equivalent to the Langhien (Orléanais), Helvétien 
(Sansan, Simorre), and Tortonien (Grive St. Alban, Bamboli) stages of 
Europe, the most exceptional progress has been made in the distinction 
of the geological and faunal zones. Ten years ago the accurate geological 
observations of Haypex were overlooked, and it was believed that forma- 
tions equivalent to the Middle and Lower Miocene of Europe were 
! The Extinct Rhinoceroses. Mem. Amer. Mus. Nat. Hist., Vol. I, 1898, pp. 75-165. 
? A New KRhinoceros, Trigonias Osborni. Proc. U. $. Nat. Mus. xxiii, No. 1207. 
$ Bull. Amer. Mus. Nat. Hist. XVI, 1902, pp. 91-109. 
* Marraew. J'ossil Mammals of the Tertiary of Northeastern Colorado. Mem. 
Amer. Mus. Nat. Hist., Vol. I, Pt. vi, 1901. 
