Journal Hafner, U.S. 1977 11 km. N, 12 km. E Arriaga, 2030 m., San Luis Potosí, México. 26 July (cont.) By 1400 we had capture 2 specimens, one alive (in the padded-MacAbee) and one dead (also in the padded-MacAbee). Results: 2 Thomomys umbrinus We took tissue and blood from the dead specimen. Then drove west to Ojuelos where we turned S on Hwy 49 toward St Dolores Hidalgo. We drove through beautiful high desert countryside (much of which was in agricultural use) and stopped occasionally to look at the small towns along the way (Ocampo, San Felipe). 1600 drove into Dolores Hidalgo. Got fuel, then continued S and W on Hwy 110 toward Guanajuato. Our next Thomomys locality is located near Santa Rosa, in the mountains NE of Guanajuato. After a long, twisting journey through the mountains we arrived in Guanajuato ca. 1730 hrs. The nearby habitat is mixed Oak-Pine forest, mostly oak. We noted occasional stands of Manzanita (Arctostaphylos). Guanajuato is a beautiful, crowded city built on the SW facing slopes of the main N-S mountain chain of the Sierra Madre Occidental. It is a colonial