Banks, RC. 1955 5. 28-31 Oct. J. Schnell + I set 10 mus. sp. I rat trap 1 mi S. 1 mi E. Onicola, 700 ft, Contra Costa Co., Calif., in field near thistles. Set 15 mus. sp. 4 rat traps in woods. Sat (29 Oct.) A.M. had 4 & Mus musculus, 3 & Reithrodontomys megalotis in field. Put up 2 Mus, 2 Reithrodontomys. (RCB 13/14/5/16.) Schnell catch I Reithrodontomys. Other Mus measured 133-62-16-12 and 121-63-17-10. The Reithrodontomys were at first believed to be some Peromyscus. The grooved upper incisors escaped notice. Ones caught last week were identified now. The Reithrodontomys were similar in color to Mus, but were lighter below and had 2-tone tail. Hair on inside of ear is darker than in Mus. There is also a lighter area on flank and a darker streak on the back in Reithrodontomys, which is lacking in Mus. No. RCB 12-16 were all caught in a line of about 50 yds. where a field of 10-12" high thick green grass joined an area of dead thistle or other composite. Walnut meat was used as bait. All specimens were caught at night.