6 
JOURNAL OF MAMMALOGY 
in the rhinoceroses and horses, as well as in other perissodactyi families 
and in the proboscideans. This mode of classification has been more 
or less widely accepted. The most debatable point is the adoption of 
the special family term ending in -ince for the phylum. For example, 
the family of rhinoceroses is divided by Osborn into six phyla,^® each 
of which is assigned a subfamily name. Similarly Osborn divides 
the Proboscidea into six phyla,^^ each of which takes a subfamily name. 
Some of these subfamilies or phyla are shown to be extremely ancient, 
to go back milfions of years, e.g., the long-jawed phyla of the Pro- 
boscidea, which goes back to the Lower Ofigocene. 
In the case of the titanotheres, extending over more than a third of 
the Tertiary period, the family is subdivided into twelve subfamilies or 
phyla, which are separated by distinct evolutionary tendencies leading 
to different extremes of structure. 
In mammalian palaeontology Merriam, Lull, Loomis, and Stock have 
been advancing both the phyletic and zoogeographic methods of 
research. 
In the meantime equally intensive observations have been made by 
Osgood, Grinnell, Nelson, G. M. Allen, Bailey, Howell, and other 
mammalogists on two very important principles of mammalogy, 
namely: 
1. Intensive , study of the relation of geographic distribution and 
vertical range on proportional characters of the skull and skeleton, 
and on the color characters of the pelage. 
2. The finking up of distinct geographic forms through geographic 
connecting intergrades. The special paper to which I allude is the 
paper by Osgood on Peromyscus. 
The latest phase of zoologic mammalogy in this country is seen in 
the work of Sumner^^ in attempting to analyze the variations of Pero- 
myscus from the standpoint of the mutation theory of DeVries, of 
20 Osborn, H. F. Phylogeny of the Rhinoceroses of Europe. Rhinoceros 
Contributions no. 5. Bull. Amer. Mus. Nat. Hist., vol. XIII, art XIX, pp. 
229-267, Dec. 11, 1900. 
21 Osborn, H. F. A Long-Jawed Mastodon Skeleton from South Dakota and 
Phylogeny of the Proboscidea. Bull. Geol. Soc. Amer., vol. 29, no. 1, pp. 
133-137, Mar., 1918. 
22 Sumner, F. B. 
The Role of Isolation in the Formation of a Narrowly Localized Race of Deer- 
Mice. Amer. Nat., Vol. LI, pp. 173-185, March, 1917. 
Genetic Studies of Several Geographic Races of California Deer-Mice. Amer. 
Nat., Vol. XLIX, pp. 688-701, Nov., 1915. 
Continuous and Discontinuous Variations and Their Inheritance in Pero- 
