272 The Mammals of Colorado 
Skull slender and slightly built, without special peculiarities 
of form ; the rostrum nearly as long as brain-case ; the depth of the 
brain-case including auditory bullae about equal to mastoid breadth ; 
sagittal crest low, but usually distinct; palate deeply emarginate in 
front, abruptly contracted behind, the sides of its posterior extension 
parallel. Auditor}' bullae well developed, but simple in form, and 
not very large. Ear well developed, slender, occasionally rather 
large; tragus slender and nearly or quite straight. Tail about as 
long as outstretched leg. Dentition, i. | ; c. ^ ; pm. f ;m. f ; X 2 =38. 
The North American members of the genus Myotis are 
all small delicately formed bats, which, aside from their 
dental formula, shared by no other American genus of 
Vespertilionidce, are usually recognized by their slender forms, 
long tails, hairy faces, narrow ears, and tapering straight 
or recurved tragi. 
The genus Myotis has a geographical distribution covering 
the entire mainland of the Eastern and Western Hemispheres 
to the limits of tree growth; also the ]\Ialay Archipelago, 
New Guinea, Australia, and Samoa, and in America the 
Lesser Antilles. About eighty species are now known, of 
which fourteen, further subdivided to form twenty-three 
subspecies, are reported from North America, and of these 
six species and subspecies have been met with in Colorado. 
Key of the Species 
A. Ear when laid forward extending less than 0.25 beyond nostril. 
a. General color whitish gray or yellowish brown. 
a'. Hind foot, 0.3 to 0.4; forearm, 1.3; color whitish gray, 
membranes pale dusky. M. yumanensis, p. 273 
b'. Hind foot, 0.2 to 0.26; forearm, 1.3; color whitish gray 
or pale yellowish brown; membranes dark. 
M. c. ciliolabrum, p. 275 
b. General color never whitish gray. 
a'. Foreann, 1.15 to 1.37 ; color light yellowish gray or brown. 
M. calif ornicus, p. 274 
b'. Forearm, 1.15 to 1.60 ; species averaging larger than under 
a'. 
a". Ear and tragus slender, the latter 0.35 or more in 
length; color light brown; forearm, 1.35. 
M. sublilatus, p. 275 
