The extensive collection of Mexican mammals made by Mr. J. R.Alcorn for the University of Kansas Museum of Natural Historycontains fourteen piñon mice from lava rocks eight miles northeastof the city of Durango, Mexico. These mice are all much darkerthan the piñon mice, Peromyscus truei gentilis, of adjoining areasin Durango and Zacatecas and show a superficial resemblance tothe widespread P. t. gratus which occurs 450 miles to the southeast.Morphological differences from P. t. gratus, as well as geographicconsiderations (see remarks), make desirable the recognition of thelava-dwelling piñon mice from Durango as a distinct subspecies.
All specimens examined of subspecies compared with the seriesof piñon mice from northeast of Durango are in the University ofKansas Museum of Natural History. Capitalized color names anddesignators are of Maerz and Paul, A Dictionary of Color, McGrawHill Book Co., New York, 1930.
I wish to acknowledge generous financial aid from the KansasUniversity Endowment Association which made possible the fieldwork by Mr. Alcorn in Mexico.
This heretofore unknown subspecies is characterized below andmay be known as:
Peromyscus truei erasmus subsp. nov.
Type.—Mus. Nat. Hist., Univ. Kansas, no. 34417, young adult female, skinand skull; from eight miles northeast of Durango, 6200 feet, Durango, Mexico;collected 16 August 1949 by J. R. Alcorn, original number 10255.
Range.—Known only from the type locality.
Diagnosis.—Upper parts dark brownish gray (Smoke Brown, 16 A 2, toBiskra, 16 A 12), darkest between ears; lower sides suffused with dull orangebuff (13 H 9 to 12 H 9); dark eye ring and black spot at base of vibrissaeconspicuous; ears 95 to 100 per cent as long as hind foot; bullae round, greatlyinflated; interparietal large, anterior margin curved or slightly sinuous, notbulging strongly forward laterally; rostrum short; nasals broad; braincase highand full; incisive foramina slightly pointed anteriorly; molars small, as inP. t. gentilis.
Measurements.—Measurements of 3 males and mean and extreme measurementsof 11 females, all from the type locality, are, respectively, as follows:[Pg 266]total length, 192, 188 (incomplete), 196 (incomplete), 193 (188-209); lengthof tail, 102, 97 (broken), 97 (broken), 101 (94-114); length of hind foot,22, 23, 23, 22.5 (22-23); length of ear, from notch, in flesh, 21, 22, 23, 21.5(20-23); greatest length of skull, 27.4, 27.7, 27.9, 27.3 (26.5-28.3); basilarlength, 20.2, 21.0, — (broken), 20.4 (19.6-21.2); greatest breadth of braincase,12.8, 12.8, 13.3, 12.85 (12.4-13.4); least interorbital breadth, 4.4, 4.6,4.6, 4.41 (4.2-4.6)