uthwest of Sun City, Barber County,
Kansas, in November. More than seasonal differences in length of pelage
is indicated by measurements of additional specimens of each subspecies
taken at different times of the year.

Considering its extensive geographic range and its occurrence in many
contrasting environments, _Myotis velifer_ varies little; and the
variation that does occur is continuous. The change from the large, dark
Mexican subspecies to the small, pale Arizonan subspecies is gradual.
The reason may lie in the ecology of _M. velifer_. It seems that there
are few barriers separating populations. Waterless areas and regions
lacking suitable roosting places such as fissures in cliffs and outcrops
of rocks, caves and buildings, may exclude the species from certain
areas, but there are few areas of any great size within the range of
the species that lack these features. Also, these bats are strong
fliers; even between fairly distant colonies there may be considerable
gene flow. The geographic variation observed probably is the result of
adaptation, on the part of populations in different parts of the range
of the species, to different environments. The lack of any effective
barriers except possibly distance between populations tends to limit
subspeciation and to cause gradual variation between subspecies. _M. v.
peninsularis_, the subspecies at the southern tip of Baja California, is
not considered in this discussion. So far as known, however, that
subspecies is completely isolated from the mainland populations of _M.
velifer_.

For the opportunity to examine specimens under their care I wish to
thank Dr. William H. Burt of the University of Michigan Museum of
Zoology, Dr. Rollin H. Baker of the Museum of Natural History of
the University of Kansas, and Dr. Donald F. Hoffmeister of the
University of Illinois Museum of Natural History. I am indebted
also to persons in charge of the Biological Surveys Collection and
the National Museum for the loan of critical material, and to Dr.
E. Raymond Hall for suggestions. The following symbols are used to
designate the source of specimens: BS--Biological Surveys
Collection, IM--University of Illinois Museum of Natural History,
KU--Museum of Natural History of the University of Kansas,
MM--University of Michigan Museum of Zoology, NM--United States
National Museum, TV--collection of Terry A. Vaughan.

_Spec