250 University of California Publications in Zoology [Vol.12 



Opposite Cibola, as already noted under P. formosus, the spiny 

 pocket mouse occurred on a broad desert wash, strewn with boulders. 

 Specimens were trapped there, not only among boulders but around 

 scraggly stumps of ironwood. 



The breeding season apparently does not begin till April. On the 

 13th and 19th of that month females taken contained four embryos 

 each. On April 28 and May 9 half-grown young were trapped. 



Lepus californicus deserticola Mearns 



Colorado Desert Jack Rabbit 



The eight specimens secured (nos. 10682-10689) came from the 

 following localities : California side : five miles below Needles, twenty 

 miles above Picacho, and near Pilot Knob ; Arizona side : Ehrenberg, 

 and five miles north of Laguna. Specimens from the two sides of the 

 river are identical as far as I can see ; and this is to be expected. For 

 although the jack rabbit belongs primarily to the desert mesas, it 

 forages also all over the flood-bottoms. I was told that this species 

 of rabbit swims strongly when forced to take to the water. 



Jack rabbits occurred through the region in 1910 in very small 

 numbers. At some stations none at all were seen, though old sign was 

 usually plentiful. The greatest numbers were observed on the mesa 

 back of Ehrenberg, but not more than half a dozen could be seen 

 during a three hours' circuit. 



Two females shot near Ehrenberg, March 28 and 29, contained two 

 and three embryos respectively. 



The weight of an adult male (no. 10682) was four pounds, four- 

 teen ounces; of an old female (no. 10683) six pounds. 



Sylvilagus auduboni arizonae (J. A. Allen) 



Arizona Cottontail 



The year of our exploration of the Colorado Valley was stated by 



the residents of the region to be an off-year for both jack rabbits and 



cottontails. Whatever the usual conditions, both kinds of rabbits were 



. unexpectedly scarce. 



The cottontails were chiefly riparian in their local distribution. In 

 fact, the only individuals seen desertwards beyond the mesquite belt 

 were in the salt-bush association closely adjacent, and (opposite The 

 Needles) up a catclaw wash not to exceed one-half mile from the river. 



