echi."
They identified the two largest (83130 and 83131) as _Perognathus
goldmani_ and the others as _Perognathus artus_. These identifications
were reasonable in the light of knowledge available in 1941, but in the
light of information presently available from the now more abundant
material it is clear that all 10 of the specimens are _P. g. artus_.
Examination (by Hall) of the specimens reveals that the differences
relied upon by Burt and Hooper to differentiate the two species are
well within the range of individual variation. For example, the
variation (5.3 to 5.6 mm.) in width of the supraoccipital is less than
in each of some other series of specimens of equal age of _P. g. artus_
from other localities.

Also, there is geographic variation in the mice here assigned to the
subspecies _P. g. artus_; skulls are smaller in the northern part of
the geographic range and become gradually larger toward the south. In
five adults from the northern part (Batopilas 3, and 26 mi. NE Choix 2)
the mean of 12.6 of the mastoidal breadth of the skull is significantly
smaller than the corresponding mean of 13.3 in 21 adults from the
southern part (32 mi. SSE Culiacan 14, and El Dorado 7). The pelage of
individuals from one and a half miles southwest of Tocuina is notably
dark both above and below; the venter is dusky rather than white. We
suppose that the darker color is a response to a dark-colored
substrate--lava and soils derived from dark lava.

_Records of occurrence_ (in each state the localities are
listed from north to south).--Chihuahua: Carimechi, Rio
Mayo, 10 U. Mich.; 1-1/2 mi. SW Tocuina [Tocuina is a
construction camp, in 1959, on NW bank of the Rio
Septentrion, and is not the Tacuina shown on some maps SE of
that River], 10 K. U.; Batopilas, 6 U. S. N. M. Durango:
Chacala (Osgood, N. Amer. Fauna, 18:55, September 20, 1900).
Sinaloa: Rancho Rosalita, 26 mi. NE Choix, 3 K. U.; 4 mi. NE
Terrero, 6 K. U.; 1 mi. S Pericos, 20 K. U.; 12 mi. N
Culiacan, 29 K. U.; 32 mi. SSE Culiacan, 20 K. U.; 6 mi. N,
1/2 mi. E El Dorado, 41 K. U.; El Dorado, 2 K. U. Sonora:
Rio "Cuchahaque," 11.3 mi. E Alamos, 5 Univ. Arizona; 9 mi.
SE Alamos, 1000 ft., 5 K. U.

We have not seen any specimens that are intergrades between _P.
goldmani_ and _Perognathus intermedius_ (subspecies _intermedius_ or
_lithophilus_), nor between _P. goldmani_ and _Perognathus nelsoni_
(subspecies