Dorado (75263); 6 mi. N, 1-1/2 mi. E El
Dorado (75264-66); 7 mi. NE El Fuerte (81076-77); and 1 mi. S Pericos
(61292-93). Specimens from the vicinity of El Dorado extend the known
range some 30 miles southward from the type locality. A female from 1
mi. S Pericos that was taken on June 13, 1954, carried three embryos
that measured 29 mm. in crown-rump length.

_=Sciurus truei=_ Nelson.--Three specimens (61300-02) of this species
collected by A. A. Alcorn on June 19, 1954, 32 mi. SSE Culiac['a]n extend
the known range approximately 210 miles south-southeast from Guirocoba,
Sonora (Burt, 1938:38), and provide the first record from Sinaloa. Two
of the specimens are females and each was pregnant, one with two embryos
and the other with three.

Our specimens generally agree in color with _S. truei_, but are larger
than typical individuals and in this respect approach _S. sinaloensis_
of southern Sinaloa. Probably _truei_ and _sinaloensis_ both are only
subspecies of the more southerly _S. colliaei_. The three nominal
species currently constitute the _S. colliaei_ group in which the
presence or absence of P3 seems to vary geographically. The tooth
frequently is absent in the northern _truei_ and usually present
(invariably in the specimens we have examined) in _colliaei_. Only one
of our Sinaloan specimens is accompanied by a skull; in it P3 is present
on the right side and absent on the left.

External measurements of the male and two females are,
respectively: total length, 512, 508, 504; length of tail, 263,
263, 252; length of hind foot, 64, 63, 64; length of ear from
notch, 28, 29, 28. Cranial measurements of 61300 (a female) are:
greatest length of skull, 56.2; zygomatic breadth, 32.6;
interorbital constriction, 17.9; postorbital constriction, 17.9;
length of nasals, 17.3; alveolar length of maxillary tooth-row (on
side lacking P3), 10.9.

_=Thomomys umbrinus atrovarius=_ J. A. Allen.--Two specimens (85104-05)
from the valley of the R['i]o Piaxtla, 1 mi. SE Camino Re['a]l, 400 ft.,
resemble the description of _atrovarius_ and agree in size, color and
most cranial details with a specimen (85744) from 5 mi. NW Mazatl['a]n. The
first-mentioned specimens extend the known range of the subspecies some
50 miles northward from Mazatl['a]n (Bailey, 1915:96), and indicate the
probable occurrence of the species at lower elevations in other parts of
central Sinaloa.

_=Peromyscus merri