162 University of California Publications in Zoology [Vol. 27 
amphibians inhabiting relatively arid situations possess a thickened 
and roughened integument. I believe that the smooth surface texture 
of the skin of Scaphiopus (which is carried to an extreme on the soles 
of the hind feet) is related to facilitating movement through the earth 
when burrowing. The surface texture of the skin of Scaphiopus com- 
pares rather favorably with that of several of the aquatic frogs; 
reduction of friction in earth and in water would seem to be a factor 
here. 
Scaphiopus, in combination with its digging equipment, has other 
characteristics which would seem to be of decided benefit to an am- 
phibian living amid arid surroundings. The voice of the male at 
spawning time is very loud, equaling or exceeding that of Hyla regilla 
and many times stronger than that of Bufo b. halophilus. Upon the 
advent of rain in amount to form pools we may expect that the first 
male Scaphiopus to enter a rain pool would begin calling ; this would 
serve to attract females and other males so that a breeding colony 
would be established quickly. Rain pools do not necessarily always 
form in the same place in successive years. If, as we have reason to 
suppose, the adults are more or less scattered when in their burrows, 
the strong voice of the first male entering a pond suitable as a breed- 
ing environment would serve to concentrate the local population there. 
Once concentrated, spawning is evidently accomplished with speed 
as indicated by the large numbers of eggs in similar stages of develop- 
ment found in the ponds near Santa Maria following the first heavy 
late spring rain . The embryonic developmental period is found to 
be short. The larval period is probably also short if we may judge 
by analogy from the known facts in the case of the other two widely 
distributed species of Scaphiopus in the United States. The newly 
transformed young spadefoot has at once the burrowing reflex of the 
species, which it must, in the case of prairie ponds lacking a border 
of aquatic vegetation as temporary shelter, put to immediate use to 
protect itself from desiccation. 
Scaphiopus hammondii has penetrated to the northern end of the 
semi-arid area in interior California (head of the Sacramento Valley), 
to the northern end of the Great Basin (southern British Columbia), 
and along the eastern base of the Rockies to eastern Montana. It 
occupies the entire area where open-surfaced rain pools are likely to 
occur. No spadefoot seems to have been found on the Great Plains of 
middle North America. The deserts of California (Mohave and Colo- 
rado) seem at the present time to be untenanted by spadefoots of any 
