GEOGRAPHIC DISTRIBUTION OF LIFE IN NORTH AMERICA. 387 
T. 8. Brandegee tells us, is sub-tropical.* This indicates the presence 
of a narrow coast belt similar to that of southern Florida, but of less 
extent. It is possible that Basilinna vantusi is sub-tropical rather than 
Sonoran, but the details of distribution of the genus are not well 
known. 
Among reptiles, about 25 peculiar species of snakes and lizards are 
believed to be restricted to the peninsula, but no peculiar genus is 
known. Three of the genera are tropical, and nine are arid Lower 
Sonoran. 
In addition to the peculiar species and sub-species of the peninsula, 
many characteristic arid Lower Sonoran forms of mammals, birds, rep- 
tiles, insects, and plants abound. Among the latter may be mentioned 
the highly distinctive Sonoran desert brush, Larrea mexicana and 
Krameria parvifolia. 
Cope includes the whole peninsula in his Lower California region, 
but other writers restrict the peculiar fauna and flora to the end of 
the peninsula south of the north foot of the mountains between La Paz 
and Todos Santos. Bryant states: ‘‘There is no more sharply defined 
faunal and floral area that occurs to me now, excepting that of islands, 
than is embraced in the region above apanedeny but he omits to name 
the forms by which it is characterized. It is evident however that 
the peculiar fauna of the peninsula of Lower California entitles it to 
rank as a minor sub-division of the Lower Sonoran zone. It is in effect 
an insular fauna of recent origin, bearing the same relation to that of 
the mainland as do several of the adjacent islands. 
The humid division of the Upper Sonoran comprises the area in the 
eastern United States commonly known as the Carolinian fauna. The 
opossum (Didelphis) here finds its northern limit, as do the so-called 
pine-mouse (sub-genus Pitymys) and the Georgian bat ( Vesperugo geor- 
gianus). Before reaching the one hundredth meridian this area grad- 
ually loses its moisture and spreads out over the Great Plains as the 
arid or true Upper Sonoran, reaching an altitude of about 4,000 feet 
along the east foot of the Rocky Mountains in the latitude of Colorado, 
and sending a tongue northward along the Missouri obliquely through 
North Dakota and into eastern Montana. Another sub-division of the 
arid Upper Sonoran occupies the greater part of the Great Basin 
between the Rocky Mountains and the High Sierra, reaching northerly 
from the upper border of the Lower Sonoran to and including the plains 
of the Columbia and Snake rivers. Another part of noteworthy 
extent is a narrow belt encircling the interior basin of California—the 
valley of the Sacramento and San Joaquin rivers—and a branch of the 
same along the coast between Monter cy and the Santa Barbara plain. 
* Brandegee, Pia Calif. Acad. Sci., 1891, 2d ser., 111, 110. 
t Walter E. Bryant in Zoe, Oct., 1891, 11, No.3, 186. See also his important ‘‘ Cata- 
logue of the Birds of Lower California,” Proc. Calif. Acad. Sci., 1889, 2d ser., 11, 237- 
320. 
