1894. _Perognathus (Chaetodipus) nelsoni_ Merriam, Proc.
Acad. Nat. Sci. Philadelphia, 46:266, September 27, type
from Hacienda La Parada, about 25 mi. NW Cd. San Luis
Potosi, San Luis Potosi.
_Distribution in Tamaulipas._--Known only from the west side
of the Sierra Madre Oriental in southwestern part of state.
Most of the specimens examined were taken in semi-arid habitats where
the dominant plants were cactus, weeds and bushes.
In Tamaulipas, specimens from the southern localities (places labeled
with reference to Tula) are darker than those from the two northernmost
localities (Miquihuana and four miles north of Jaumave). Most
measurements are about equal in the southern and northern specimens,
but in some measurements southern specimens average slightly smaller
than those from the north. Greatest length of skull is a case in point.
The difference in size is reflected in the weights. Average weights of
nine males and nine females from southern localities are, respectively,
14.7 (12-16.5) and 13.8 (12-15.5) instead of 18.5 (17-20) and 17.0
(15-18) grams for four males and six females from the northern
localities. In general, Tamaulipan specimens average somewhat smaller
than those from other localities in eastern Mexico (see measurements
given by Baker, 1956:238, Dalquest, 1953:107, and Osgood, 1900:53).
_Measurements._--Average and extreme measurements of six
specimens (2 males and 4 females) from Miquihuana, three
males from four miles north of Jaumave, and five (3 males
and 2 females) from nine miles southwest of Tula are,
respectively, as follows: 176.2 (163-185), ----, 170, 173,
(4 specimens only) 179.0 (165-186); 99.8 (97-105), ----, 90,
93, (4 specimens only) 96.7 (88-104); 22.5 (21-23), 23, 23,
24, 22.6 (22-23); 8 (8), 8, 8, 8, 8.8 (8-9); greatest length
of skull, 26.1 (25.6-26.6), 25.8, 26.5, 26.9, 25.2
(24.9-25.7); mastoid breadth, 13.3 (12.9-13.6), 13.2, 13.8,
13.6, 13.1 (12.9-13.4); interorbital constriction, 6.4
(6.1-6.6), 5.9, 6.3, 6.3, 6.3 (6.1-6.8); interparietal
breadth, 7.4 (6.8-7.9), 7.7, 7.2, 7.2, 7.6 (7.3-7.9);
alveolar length of maxillary tooth-row, 3.7 (3.5-4.0); 3.6,
3.5, 3.6, 3.6 (3.5-3.8).
_Records of occurrence._--Specimens examined, 42:
Miquihuana, 6300 ft., 7; 4 mi. N Jaumave, 2500 ft., 5;
Nicolas, 56 km. NW Tula, 5500 ft., 10; Tajada, 23 mi. NW
Tula, 5200 ft., 6; 8 mi. N Tula, 4500 ft., 1; 9 mi. SW Tula,
3900 ft., 13.
Additional record: Jaumave (Miller, 1924:284).
=Dipodomys ordii=