ALLEN* — BATS FROM NEW MEXICO AND ARIZONA 
161 
Nyctinomus mexicanus (Saussure) 
MEXICAN FREE-TAILED BAT 
This is probably the most abundant bat in the territory under con- 
sideration. As is well known^ it is highly gregarious^ living in colonies 
often of large size. So ready is it to take advantage of the shelter 
offered by human habitations, that colonies are more often found in 
the recesses of a roof than in caves, the primitive habitation. Mr. 
Huber discovered one cave fifteen miles northwest of Las Cruces, 
New Mexico, that was inhabited by this species. Twelve individuals 
taken at random here on June 2, proved to be all adult females, each 
with a good-sized fetus. At Bevino, there was a large colony living 
in the hollow space beneath a roof, entrance to which was gained through 
a crack over a door. Mr. Huber gathered 67 here on June 8, of which 
about one fourth were adult males, and the rest adult females, each 
containing a single fetus. In nearly every case the fetus was large and 
would probably have been mature in another week; a few, however, 
were smaller than the rest, while one or two were larger and seemed 
almost ready for extrusion. On the whole, however, the size of the 
embryos was rather uniform and indicates that in this colony at least, 
the breeding season is at a quite definite time. In most cases the fetus 
was carried transversely to the main axis of the body, with the head 
at the right-hand side, directed forward, and the little wings folded 
over the face. 
The disproportionately small number of adult males seems typical 
of a breeding colony of this species. Mrs. Grinnell records a colony 
examined in San Jose, California, on February 2, in which the propor- 
tions of the sexes were about equal in clusters found behind the iron 
window shutters on the west side of a building; while on March 3, of 
35 specimens from behind shutters on the east side of the same building 
all were females. 
REFERENCES 
Allen, J. A. 1895. On a collection of mammals from Arizona and Mexico, 
made by Mr. W. W. Price, with field notes by the collector. Bull. 
Amer. Mus. Nat. Hist., voL 7, p. 193-258. 
1896. On mammals collected in Bexar County and vicinity, Texas, by Mr. 
H. P. Attwater, with field notes by the collector. Bull. Amer. Mus. 
Nat. Hist., vol. 8, p. 47-80. 
Elliot, D. G. 1904. The land and sea mammals of Middle America and the 
West Indies. Publ. Field Columbian Mus., zool. ser., vol. 4, pt. 2, 
p. i-xiii, 441-850, pi. 42-68. 
