92 DEUXIÈME ASSEMBLÉE GÉNÉRALE 
and Marrnew)'. Third,the polyphyletic law is the result of local adaptive 
radiation or divergence apparently of habit either by choice or by neces- 
sity. For example, among the horses it separates off the grazing types 
(Protohippus), which are naturally progressive, from the browsing types 
(Hypohippus), which are naturally conservative, both found in the same 
locality (Fig. 4). It thus splits up animals living in a single region 
into a number of contemporaneous types or genera which may coexist 
throughout long periods; it is a segregation, functional rather than adap- 
tive. Fourth,the polyphyletie law results from the invasion into a region 
of a generic or specific phylum which has evolved on another continent; 
for example, the Eurasiatic T'eleoceras came in among the American 
rhinoceroses in the Middle Miocene (Plate VIT). 
This polyphyletic law has now been demonstrated (OsBorx ?) among 
the rhinoceroses both of Eurasia and of North America, and is the key 
to the comprehension of this group; in Fig. 3 printed herewith it is 
shown that there are not only three families, namely, cursorial (Hyra- 
codontidæ), aquatic (Amynodontidæ), and terrestrial (Rhinocerotidæ), but 
that the last family splits up into six and possibly seven phyla, many of 
which are contemporaneous; and the tendency of discovery will be to 
increase rather than to diminish the number of contemporaneous inde- 
pendent phyla. Similarly the Eocene titanotheres instead of forming a 
successive monophyletic series, divide into four distinct phyla, to each of 
which a generic name must be given. Similarly, again, the lower Oligo- 
cene titanotheres‘, as shown in Fig. 7, divide into four phyla, three of 
which have been traced in successive stages from the bottom to the 
summit of the Oligocene, each giving off several collaterals, all living in 
the same region and found in contiguous beds, but probably having a 
slightly different local habitat and habits. The law is illustrated again, as 
shown in Fig. 4, both in the Oligocene and Miocene horses: in the 
Oligocene, for example, we have five contemporaneous lines of horses 
(OsBorx ”, Ginzey), one of which includes the classic Mesohippus bairdi 
of Lerpy, which was long considered the single Oligocene horse, and fi- 
gured as such in all phylogenies; in the Upper Miocene beside the Pro- 
* The Ancestry of Certain Members of the Canidæ, the Viverridæ and Procyo- 
nidæ. Bull. Amer. Mus. Nat. Hist., Vol. xii, 1899, pp. 139-148. 
? Phylogeny of the Rhinoceroses of Europe. Bull. Amer. Mus. Nat. Hist., Vol. xiii, 
1900, pp. 229-267. 
# New Miocene Rhinoceroses with Revision of Known Species. Bull. Amer. Mus. 
Nat. Hist., Vol. xx, 1904, pp. 307-326. 
# The Four Phyla of Oligocene Titanotheres. Bull. Amer. Mus. Nat. Hist., Vol. xvi, 
Feb. 1902, pp. 91-109. 
5 New Oligocene Horses. Bull. Amer. Mus. Nat. Hist., Vol. xx, May, 1904, pp. 167-179. 
