894 The American Naturalist. [November, 
Baird’ divided this region into three districts, which he 
termed the eastern, central and western. The eastern occupied 
eastern North America to the central plains, where they exceed 
800 feet above sea-level. The western included the territory be- 
tween the Cascade and Sierra Nevada Mountains and the Pa- 
cific Ocean. In my paper of 1875, I adopted the eastern, central 
and western districts (calling the last the Pacific), and proposed 
two other districts, viz.: the Austroriparian for the Louisian- _ 
ian division of the eastern of Verrill, and the Sonoran for the 
southwestern and Mexican Plateau faune. Merriam, in 1890,‘ 
proposed a different arrangement. Using the name Sonoran 
for the entire Medicolumbian Region he divided it into “ (1) 
an Arid or Sonoran subregion proper, occupying the table- 
land of Mexico, reaching north into western Texas, New Mexico, 
Arizona, and southern California; (2) a Californian subregion, © 
occupying the greater part of the State of that name; (3) a 
Lower Californian subregion ; (4) a Great Basin region, occupy- 
ing the area between the Rocky Mountains and the Sierra 
Nevada, extending as far north as the plains of the Columbia ; 
(5) a Great Plains subregion, occupying the plains east of the 
Rocky Mountains, and extending north to the plains of the 
Saskatchewan; and (6) a Louisianian or Austroriparian sub- 
region, occupying the low-lands bordering the Gulf of Mexico 
and the Mississippi, and extending eastward south of the 
Alleghanies to the Atlantic seaboard, where it reaches as far 
north as the mouth of Chesapeake Bay.” According to his ar- 
rangement the Eastern Region of Baird and myself is not 
mentioned. 
This classification may be applicable to birds and mammals; 
but it is not applicable to the fishes, Batrachia and Reptilia, 
which are much more exact indicators of the histories of faunse, 
owing to their inferior powers of migration. The eastern dis- 
trict or subregion is more nearly allied, from this point of view, 
to the Austroriparian than the latter is to the Sonoran proper, 
or arid region. This is due, as Baird previously pointed out, 
2 Amer. Jour. Sci. Arts, XCI, 1866, p. 82. 
3 Bulletin U.S. Natl. Museum, I, 1875, p. 55. 
4N. American Fauna, 1890, No. 3, p. 24. 
