238 University of California Publications in Zoology [Vol. 12 



slough five to eight feet, then gone back a third of the way and 

 started a branch to the water for another entrance. After finishing 

 that, it had come half way back on the branch and dug another branch 

 from it inland, then a branch from that to the water again. Roughly 

 speaking, a series of connected Y's thus resulted, with ends alter- 

 nately in the water and in the bank landwards. It would appear as 

 though such a plan of runways were well adapted to eluding enemies, 

 both terrestrial and aquatic. An adult male and two two-thirds-grown 

 young were trapped in the entrance burrows. 



In the vicinity of Pilot Knob tl.? muskrats were living along the 

 steep northern bank of the main river, where the water was overhung 

 by a dense growth of cane. A number of willow branches sagging 

 into the water and drift logs caught in the tangle of cane (pi. 4, fig. 3) 

 showed themselves to be the nightly rendezvous of muskrats. On 

 these, at the farthest projecting portions, and usually not over four 

 inches above the surface of the water, capsule-shaped pellets of excre- 

 ment to the number of three to a dozen or more marked the perching 

 places of the rats. This excrement was usually fresh, as the logs would 

 go awash with the frequent cross-river winds. Number steel traps 

 set on these logs without attempt at concealment, either with or with- 

 out bait (apple or potato), caught five adult muskrats. May 10 to 14. 

 Four out of the five were drowned, the traps being provided with 

 chains which in turn were nailed to the logs. A half-growii youngster 

 was shot on the latter date as it swam among some trailing cane stalks. 



Muskrats have recently invaded the Imperial Valley along the 

 irrigation canals leading from the Colorado River. I visited this 

 valley in February, 1912, and was told there that the California Devel- 

 opment Companj^ found it necessary to hire men to shoot and trap 

 muskrats because of the damage done in burrowing through the 

 levees. The rats even follow the smaller ditches out into the farms 

 at Calexico. Heber, and El Centro. At Calexico, February 8, I 

 obtained a fresh specimen shot by a boy on a farm close by, on the 

 California side of the Mexican boundary. 



The entire series of ten specimens of the pallid muskrat in the 

 Museum displays the now well-known features peculiar to the race 

 represented, namely, small size, pale color and relatively scanty pelage 

 (see Mearns, 1907, p. 495). The weights of the five full-grown male 

 animals were: 31, 24, 21, 26, and 27 ounces, respectively; average 

 26 ounces. 



