/^ Vol. 52, pp. 147-150 October 11, 1939 PROCEEDINGS Oy THE BIOLOGICAL SOCIETY OF WASHINGTON DESCRIPTIONS AND RECORDS OF HARVEST MICE (GENUS REITHRODONTOMYS) FROM MEXICO. BY SETH B. BENSON, Museum of Vertebrate Zoology, University of California. Harvest mice collected in northern Mexico in the past three years include Reithrodontomys montanus Baird, formerly not known to occur in Mexico, and two undescribed forms, one a species belonging to the subgenus Reithrodontomys, the other a race of Reithrodontomys fulvescens Allen. Reithrodontomys burti, new species. Type. — Adult male, skin and skull, no. 83001 Mus. Vert. Zool., collected at Rancho de Costa Rica, Rio Sonora, Sonora, Mexico, on May 3, 1938, by Margarito Delgadillo. Original number 5400 Seth B. Benson. Distribution. — Coastal flood plains of western Sonora from the Rio Sonora south to near Guaymas. Diagnosis. — A member of the subgenus Reithrodontomys (as defined by HoweU, U. S. Dept. Agr., Bur. Biol. Surv., N. A. Fauna No. 36, 1914) characterized by small size, short tail, relatively short hind feet, large ears, pale color, yellowish cheeks, distinct light-colored area surrounding ear, conspicuous pale tuft at anterior base of ear, nearly pigmentless tail, angular skull, abruptly spreading zygomata, large infraorbital foramina, long (7.3 mm.) nearly straight baculum. Comparisons. — Distinguished from all species of Reithrodontomys save R. montanus Baird, R. megalotis Baird, and R. humidis Bachman, in having, on the average, a tail less than 65 mm. in length and shorter than length of head and body. Compared with R. montanus (as defined by Benson, Joum. Mammalogy, vol. 16, 1935, pp. 139-142) : Similar in size and proportions except for ears which are much larger. Color paler, of yellowish cast rather than grayish. Cheeks paler and more strongly contrasted with color on top of head. Tail with less pigment, lacking the sharply distinct dark dorsal stripe present in montanus. Skull larger, nasals relatively longer, zygomata more angular and spreading more widely anteriorly, infraorbital foramina distinctly 36— Proc. Biol. Soc. Wash., Voi,. 52, 1939. (147)
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