_Peromyscus pectoralis_ and _P. boylii_ are closely related
morphologically and seem to occupy the same habitat. In the Sierra
Madre Oriental, according to the field notes of the collector
(Heinrich, June 6 to August 5, 1953), individuals of _P. pectoralis_
had a pinkish coloration on the mouth and forefeet produced by the
juice of the "nopal" cactus fruit, on which obviously the mice feed,
whereas only a few specimens of _boylii_ were thus discolored. It was
noted that _boylii_ was feeding on acorns. Furthermore, the two species
may differ in time of breeding; in August, males of _pectoralis_ had
the testes well developed when those organs were small in _boylii_
collected at the same locality.
A specimen from 53 kilometers north of El Limon, was shot at a height
of 10 feet on a concrete underpass. Other specimens were taken in a
trap line that yielded _Peromyscus boylii_, _P. leucopus_ and _Liomys
irroratus_.
Two subspecies of _P. pectoralis_ occur in Tamaulipas: _P. p. collinus_
is widely distributed in the central and western parts of the state and
_P. p. eremicoides_ occurs only in the western "corner" of the state.
=Peromyscus pectoralis collinus= Hooper
1952. _Peromyscus pectoralis collinus_ Hooper, Jour. Mamm.,
33:372, August 19, type from San Jose, 2000 ft., Sierra San
Carlos, 12 mi. NW San Carlos, Tamaulipas.
_Distribution in Tamaulipas._--Along the central and western
mountains.
A female obtained on January 21 at a place 53 kilometers north of El
Limon, contained three embryos. A lactating female was taken on August
2 in the Sierra Madre Oriental. Males, as previously noted, had
well-developed testes in August. The weights of 17 males and 20 females
from the Sierra de Tamaulipas were, respectively, 26.6 (24-33), and
25.6 (21-31) grams.
Measurements of specimens from different localities in Tamaulipas
averaged about the same, except that those of specimens from Palmillas,
averaged smaller. The small size suggests intergradation between the
subspecies _collinus_ and _eremicoides_. The latter occurs to the west
and differs from _collinus_ in smaller size, more grayish coloration,
completely white tarsal joint and relatively longer tail. Hooper
(1952:374) reported specimens from Jaumave as intergrades between the
two subspecies before mentioned and Osgood (1909:164) identified two
specimens from there as _eremicoides_. In the present account,
individuals from Palmillas and Jaumave are referred to _collinus_.
_Records of occurrence._--Specimens examined, 101: 7 km. SW
La Purisima, 1; Sierra Madre Oriental, 5 mi. S, 3 mi. W
Victoria, 1900 ft., 12; Sierra Madre Oriental, 8 mi. S, 6
mi. W Victoria, 4000 ft., 16; Sierra de Tamaulipas, 2 mi. S,
10 mi. W Piedra, 1200 ft., 36; Sierra de Tamaulipas, 3 mi.
S, 14 mi. W Piedra, 1200 ft., 14; 14 mi. N, 6 mi. W
Palmillas, 5500 ft., 1; Palmillas, 4400 ft., 3; 53 km. N El
Limon, 12 km. S Rio Guayalejo, 5; Joya Verde, 35 km. SW
Victoria, 3800 ft., 9; 10 km. N, 8 km. El Encino, 400 ft.,
1; 8 km. NE Antiguo Morelos, 500 ft., 3.
Additional records (Hooper, 1952:374, unless otherwise
noted): Sierra San Carlos (Marmolejo, 1700 ft., San Jose,
2000 ft., Tamaulipeca, 1500 ft., La Vegonia, 2900 ft.);
Villagran, 1300 ft.; Cd. Victoria; near Jaumave, 2400 ft.;
Sierra de Tamaulipas, near Acuna, 1600 ft.; La Joya de Salas
(Goodwin, 1954:12).
=Peromyscus pectoralis eremicoides= Osgood
1904. _Peromyscus attwateri eremicoides_ Osgood, Proc. Biol.
Soc. Washington, 17:60, March 21, type from Mapimi, Durango.
1909. _Peromyscus pectoralis eremicoides_, Lyon and Osgood,
Bull. U. S. Nat. Mus., 62:128, January 28.
_Distribution in Tamaulipas._--Known only from Miquihuana
and vicinity of Tula.
The two specimens from Miquihuana are typical _P. pectoralis
eremicoides_ in external and cranial measurements. Specimens from nine
miles southwest of Tula are characteristic of _eremicoides_ in cranial
measurements but the tail is shorter than usual for this subspecies, in
this respect approaching _P. p. lacianus_.
_Measurements._--Average and extreme measurements of 10
specimens from nine miles southwest of Tula and measurements
of two males (56169, 56415) from Miquihuana are,
respectively, as follows: 181.5 (173-197), 180, 197; 96.2;
(87-110), 103, 113; 20.2 (19.0-21.5), 21, 21; 18.1
(16.5-19.0), 18, --; greatest length of skull, 24.8
(24.1-25.6), 25.5, 25.6; length of nasals, 9.0 (8.6-9.3),
9.3, 9.3; zygomatic breadth, 12.2 (11.7-12.8), 12.3, 12.9;
interorbital constriction, 3.8 (3.7-4.0), 3.7, 3.9; length
of maxillary tooth-row, 3.6 (3.5-3.7), 3.6, 3.8. Weights of
the 10 specimens from nine miles southwest of Tula average
17.9 (16-24) grams.
_Records of occurrence._--Specimens examined, 28:
Miquihuana, 6200 ft., 2; Nicolas, 56 km. NW Tula, 5500 ft.,
1; Tajada, 23 mi. NW Tula, 5200 ft., 1; 8 mi. N Tula, 4500
ft., 2; 9 mi. SW Tula, 3900 ft., 19; 17 mi. SW Tula, 3900
ft., 3.
=Peromyscus melanophrys consobrinus= Osgood