Two New Meadow Mice from Michoacán

Mexico

Type.—Male, adult, skin and skull; No. 100637, Univ. California Mus. Vert.
Zool.; 3½ mi. S Pátzcuaro, 7,900 ft., Michoacán, México; March 9, 1943; obtained
by E. R. Hall, original no. 5882.

Range.—Known only from the vicinity of the type locality.

Diagnosis.—Size large (see measurements); color brown overlain with cinnamon;
nasals expanded distally with premaxillary borders concave laterally;
posterior border of orbit inclined posterolaterally; preorbital region and
interparietal region depressed; incisive foramina narrow; zygomatic arches
parallel; tympanic bullae much inflated.

Comparisons.—Among named subspecies of Microtus mexicanus, M. m.
fundatus most closely resembles M. m. mexicanus but differs as follows: Larger
in all parts measured; pelage with slightly less buffy color and with the buffy
color that is present of a slightly lighter tint; posterior two-thirds of premaxillary
border of each nasal concave rather than straight; posterior border of
orbit forming more acute angle with sagittal plane of posterior part of skull;
superior outline of nasals straight rather than depressed in posterior part;
tympanic bullae more inflated both in vertical and horizontal planes.

From M. c. salvus, the subspecies next to the westward, fundatus differs as
follows: Averaging larger in all parts measured; less reddish on upper parts;
underparts with more reddish color but the reddish of lighter tint; perineal
region buffy instead of plumbeous; nasals with premaxillary borders laterally
concave rather than straight; superior outline of skull with nasal segment
sloping anteroventrally and interparietal segment sloping posteroventrally
rather than straight; posterior margin of orbit inclined posterolaterally thus
forming an acute angle, instead of a right angle, with sagittal plane of braincase;
zygomatic arches parallel rather than bowed outward; incisive foramina
narrower; tympanic bullae more inflated in vertical plane.

Relying on Bailey's (N. Amer. Fauna, 17:55, 1900) description of Microtus
fulviventer, fundatus differs in much larger tympanic bullae.

Specimens examined.—Total, 59, distributed, with respect to the town of Pátzcuaro, as
follows: 3½ mi. S, 7,900 ft., 9; 4 mi. S, 7,800 ft., 16; 5 mi. S, 7,800 ft., 26; 9 mi. SE,
8,000 ft., 8.

Type.—Female, adult, skin and skull; No. 52099, Chicago Natural History
Museum; Mount Tancitaro, 11,400 ft., Michoacán, México; July 19, 1941;
obtained by F. C. Wonder, original No. 1163.

Range.—Known only from Mount Tancitaro at elevations of 7,800 to 11,400
feet.

Diagnosis.—Size medium (see measurements); color brown overlain with
cinnamon; premaxillary borders of nasals straight; superior outline of skull
nearly straight; posterior margin of orbit at right angle with long axis of skull;
zygomatic arches bowed outward; incisive foramina wide; tympanic bullae
small.

Comparisons.—From topotypes of its nearest relative, Microtus mexicanus
phaeus Merriam, salvus differs as follows: Tail shorter; pelage with slightly
more buffy (reddish) pigment which, nevertheless, is of a lighter tint; premaxillary
borders of nasals straight rather than concave; superior outline of
skull more nearly straight (less convex); inferior border of rostrum more
nearly straight (less concave distally); palatal fossae uniformly shallower.

Comparison with M. m. fundatus is made in the account of that subspecies.

Specimens examined.—Total, 14, from Mount Tancitaro, Michoacán, distributed, according
to elevation above sea level, as follows: 11,400 feet, 8; 11,000 ft., 2; 7,800 ft., 1; no
elevation recorded, 8.

Measurements of the two subspecies.—Average and extreme measurements
of ten adult males of M. m. fundatus and eight adult males of M. m. salvus,
are, respectively, as follows: Total length, 147 (135-158), 141 (134-146); length
of tail, 33.4 (30-39), 29.6 (25-32); length of hind foot, 21.1 (20-22), 20.0 (18-21);
condylobasal length, 27.7 (27.0-29.0), 25.9 (25.5-26.2); occipitonasal length, 27.5 (26.8-28.5),
25.7 (25.3-26.0); length of nasals, 8.0 (7.7-8.4), 7.5 (6.9-8.1); zygomatic
breadth, 16.4 (15.9-17.2), 15.0 (14.6-15.3); interorbital breadth, 3.7 (3.5-3.9), 3.5 (3.3-3.6);
mastoid breadth, 12.7 (12.2-13.2), 11.7 (11.7-11.7); alveolar length of
upper molar series, 7.0 (6.8-7.3), 6.7 (6.5-6.9); width of rostrum, 5.7 (5.1-5.9),
5.3 (5.3-5.3); palatilar length, 13.3 (12.7-14.3), 12.6 (11.9-12.9). Of M. m. salvus
only two specimens yield data for the first, second, sixth and eighth cranial
measurements named above.