ncial aid from the Kansas
University Endowment Association which made possible the field
work by Mr. Alcorn in Mexico.

This heretofore unknown subspecies is characterized below and
may be known as:

=Peromyscus truei erasmus= subsp. nov.

_Type._--Mus. Nat. Hist., Univ. Kansas, no. 34417, young adult female, skin
and skull; from eight miles northeast of Durango, 6200 feet, Durango,
Mexico; collected 16 August 1949 by J. R. Alcorn, original number 10255.

_Range._--Known only from the type locality.

_Diagnosis._--Upper parts dark brownish gray (Smoke Brown, 16 A 2, to
Biskra, 16 A 12), darkest between ears; lower sides suffused with dull
orange buff (13 H 9 to 12 H 9); dark eye ring and black spot at base of
vibrissae conspicuous; ears 95 to 100 per cent as long as hind foot; bullae
round, greatly inflated; interparietal large, anterior margin curved or
slightly sinuous, not bulging strongly forward laterally; rostrum short;
nasals broad; braincase high and full; incisive foramina slightly pointed
anteriorly; molars small, as in _P. t. gentilis_.

_Measurements._--Measurements of 3 males and mean and extreme measurements
of 11 females, all from the type locality, are, respectively, as follows:
total length, 192, 188 (incomplete), 196 (incomplete), 193 (188-209);
length of tail, 102, 97 (broken), 97 (broken), 101 (94-114); length of hind
foot, 22, 23, 23, 22.5 (22-23); length of ear, from notch, in flesh, 21,
22, 23, 21.5 (20-23); greatest length of skull, 27.4, 27.7, 27.9, 27.3
(26.5-28.3); basilar length, 20.2, 21.0, -- (broken), 20.4 (19.6-21.2);
greatest breadth of braincase, 12.8, 12.8, 13.3, 12.85 (12.4-13.4); least
interorbital breadth, 4.4, 4.6, 4.6, 4.41 (4.2-4.6); length of nasals,
10.1, 10.3, 10.9, 10.3 (9.8-11.1); diastema, 6.6, 7.0, 7.1, 6.78 (6.3-7.2);
length of incisive foramina, 5.6, 5.9, 6.0, 5.77 (5.5-6.0); length of
palatal bridge, 3.8, 3.9, --, 3.96 (3.8-4.3); postpalatal length, 9.9, --,
--, 9.7 (9.2-10.4); alveolar length of maxillary tooth-row, 4.1, 4.1, 4.4,
4.2 (4.1-4.4). All measurements are in millimeters.

_Measurements of the type._--Total length, 189; length of tail, 95; length
of hind foot, 22; length of ear, from notch (in flesh), 21; greatest length
of skull, 26.9; basilar length, 20.3; greatest breadth of braincase, 13.0;
least interorbital breadth, 4.4; length of nasals, 10.1; diastema, 6.6;
length of incisive foramina, 5.5; length of palatal bridge, 3.9;
postpalatal length, 9.8