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University of California Publications in Zoology [Vol. 27 
populations to the north by the salt water of San Francisco Bay. 
Due to the lack of suitable environmental conditions for these species 
by way of land around the eastern margin of the bay, San Francisco 
Bay and the Golden Gate may be said to constitute, at the present 
time, a barrier limiting their range. In the case of the island species, 
Aneides l. farallonensis, Batrachoseps pad ficus, and B. catalinae, the 
salt water is an effective barrier, separating them from the mainland 
stocks to which they are most closely related. 
No amphibian in California is limited by permanently frozen 
ground and, indeed, in North America generally there are at most 
only two species limited by that barrier. Five species of California 
amphibians occur in the Sierra Nevada up to altitudes of 10,000 feet 
or higher and thus have to meet ‘boreal’ conditions. These are Hydro- 
mantes platycephala, Bufo boreas halophilus, Bufo canorus, Hyla 
regilla, and Rana boylii sierrae. In the high altitudes reached or 
inhabited by these species there is a period of from several weeks to 
several months during the winter when low temperatures prevail. 
The frog (Rana), judging from its habits in summer, probably 
winters, like its overwintering larva, in the unfrozen water in the 
depths of the glacial lakes. The other species, which are primarily 
terrestrial in their habits, probably overwinter in holes in the ground 
or in crevices in rock slides. To judge from the amount of winter- 
time activity manifested by pocket gophers in the boreal portions of 
the Sierra Nevada (see Grinnell and Storer, 1924, pp. 139-140), there 
is but slight freezing of the ground. Hence, by retiring but a short 
distance below the surface these amphibians would be able to escape 
freezing. In the lower altitudes in California there is practically no 
danger to amphibians from freezing temperatures (see accounts of 
Rana aurora draytonii and Rana boylii boylii). 
Complete deserts such as the Sahara of Africa and the Great 
Interior Desert of Australia are effective barriers to the spread of 
amphibians. The ‘American deserts,’ however, are inhabited in spots 
by several species of amphibians. Thus Hyla regilla occurs in several 
of the mountain ranges in eastern California; Hyla arenicolor lives 
in mountain canons from Texas to California; Bufo punctatus is 
found in Death Valley and has been recorded from a canon in the 
Turtle Mountains and in canons on the west side of the Colorado 
Desert. Other species occur locally in the desert portions of Nevada, 
