d skull of which prevents
conclusive identification. The specimen is either _M. montanus_ or _M.
mexicanus_, and is from Nutria, on the southern edge of the Zuni
Mountains (USBS). Detailed comparison of _fusus_ and _arizonensis_ is
not attempted here although it may be stated that in several characters
_fusus_ is intermediate between _arizonensis_ to the south and _nanus_
to the north.

_Specimens examined._--Total, 89, distributed as follows
(abbreviations for collections are given in the account of _M. m.
nanus_; localities that are not represented in Fig. 1 because
overlapping or crowding of the symbols would result are
Italicized):

COLORADO: _Pitkin Co._: 5 mi. W Independence Pass, 11,000 ft., 1
(Chi). _Lake Co._: _Independence Pass, 12,095 ft._, 2 (Chi).
_Gunnison Co._: _Gothic_, 2 (USBS); Decker's Ranch, Crested Butte,
2 (AMNH); Almont, 3 (USBS). _Montrose Co._: Coventry, 5 (USBS 4,
AMNH 1). _Saguache Co._: Cochetopa Pass and environs, 44 (USBS
22). _Hinsdale Co._: Ruby Lake, 1 (USBS). _Mineral Co._: 3 mi. E
Creede, 1; 23 mi. S, 11 mi. E Creede, 9300 ft., 7. _La Plata Co._:
Florida, 6800 ft., 1. _Conejos Co._: 1 mi. S, 19 mi. W Antonito,
10,200 ft., 3; _4 mi. S, 23 mi. W Antonito_, 1; _5 mi. S, 24 mi. W
Antonito, 9600 ft._, 9.

NEW MEXICO: _Rio Arriba Co._: 6 mi. W Hopewell, 9900 ft., 6 (USBS);
_Tusas River, 8700 ft._, 1 (USBS).

TABLE 1. AVERAGE MEASUREMENTS, IN MILLIMETERS, OF ADULTS OF MICROTUS
MONTANUS.

Key to column headings:

A: No. of individuals averaged
B: Total length
C: Length of tail
D: Length of hind foot
E: Condylobasilar length
F: Alveolar length of upper molar tooth-row
G: Zygomatic breadth
H: Lambdoidal breadth
I: Prelambdoidal breadth

=========================================================================
Locality | A | B | C | D | E | F | G | H | I
------------------+------+-----+-----+-----+-----+-----+-----+-----+-----
| _M. m. codiensis_, all
|
Average | 34 |165.3|44.2 |19.6 |25.47| 6.56|15.55|12.05|8.76
2 x stand. error | | 3.56| 1.84| .395| .308| .067| .198| .144|.129
Coeff. variab | | 6.0|11.6 | 5.6 | 3.5 | 3.0 | 3.65| 1.20|1.47
------------------+------+-----+-----+-----+-----+-----+-----+-----+-----
| _M. m. nanus_, Eastern Idaho
|
A