Spermophilus mexicanus parvidens Mearns
Mexican Ground Squirrel
1896. Spermophilus mexicanus parvidens Mearns, Preliminary diagnoses of new mammals from the Mexican border of the United States, p. 1, March 25, type from Fort Clark, Kinney Co., Texas.
Distribution in Tamaulipas.—Northern part of state, south at least to Xicotencatl.
Most of the specimens examined from Tamaulipas are in the brown phase (Howell, 1938:121) and differ from S. m. parvidens from Texas, Coahuila, and Nuevo León in being darker dorsally. Nevertheless, some individuals are as pale as those examined from the mentioned states. Measurements of Tamaulipan specimens average smaller than those given by Howell (1938:121) and Baker (1956:205) for parvidens.
Specimens from San Fernando differ slightly from those from Soto la Marina in having a relatively long tail (average 69.2 instead of 62.1 per cent of length of head and body) and in having the upper parts of the hind feet ochraceous instead of nearly white.
Two May-taken females from Soto la Marina carried 5 and 7 embryos that were 10 mm. in crown-rump length; another taken there was lactating. Weight of six non-pregnant females from San Fernando averaged 160.6 (129-197) grams. Two males from the same locality weighed 164 and 145 grams.
Measurements.—Average and extreme measurements of four males and three females from Soto la Marina are, as follows: 312.6 (296-330); 119.8 (110-130); 41.6 (38-43). Average cranial measurements of five specimens (two males, three females) from same locality are: greatest length of skull, 44.7 (43.7-47.4); zygomatic breadth, 26.9 (25.3-28.6); breadth of braincase, 19.4 (19.2-19.5); interorbital constriction, 13.3 (12.5-14.1); length of nasals, 15.9 (14.6-17.5); length of maxillary tooth-row, 8.3 (8.0-8.5).
Records of occurrence.—Specimens examined, 20: San Fernando, 180 ft., 12; Soto la Marina, 500 ft., 8.
Additional records (Howell, 1938:121 unless otherwise noted): Nuevo Laredo; Mier; Camargo; Reynosa; Bagdad; Victoria; Xecotencatl [= Xicotencatl] (J. A. Allen, 1891:223).