348 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Skull.— The small delicate skull is notable for its weak canines, the 
short and contracted rostrum. In the other races of this group the 
roots of the upper canines cause a distinct bulge in the outline of 
the snout as viewed from above, but in these small Mexican bats the 
gently convex and tapering outline is not noticeably interrupted. In 
contrast with the other races of megalotis the inner upper incisor is 
normally provided with a distinct pointed cusp at its outer side. This 
cusp is wanting in but one (91930, Biol. Surv. Coll.) among eighteen 
skulls from Mexico that I have examined. Mr. G. S. Miller, Jr., 
(1897, p. 53, fig. 10) records variation in respect to this cusp in a series 
from Guanajuato, in which both extremes of development are repre- 
sented. The small size of the skull, and the short tapering rostrum 
distinguish it at a glance from macrotis. 
Measurements.— The type measures: forearm 39.4 mm. (average 
of ten topotypes 4121); digit III, metacarpal 37 (average of ten topo- 
types 37.9); first phalanx 12 (average of ten topotypes 12.1); second 
phalanx 16 (average of ten topotypes 16.8); tibia 18 (average of ten 
topotypes 18.6). 
Skull: greatest length 15.6 mm.; basal length 12.5; palatal length 
7; zygomatic breadth 8; interorbital constriction 3.4; mastoid 
breadth 9; width of brain case 7.6; upper tooth-row 6; lower tooth- 
row 6.2. 
Remarks.— This small dark form from the Mexican highlands has 
till now been confused with pallescens of western United States. The 
series of skins at present available, however, shows that it is quite 
different in color, a very smoky appearing bat, nearly uniform in tint, 
with none of the buff or brown tones of pallescens or townsendi, nor 
the white belly of macrotis. In fall and winter pelage it seems to 
resemble pallescens more closely but is darker. It is odd that the 
accessory cusp of the inner upper incisor, usually wanting in other 
races of megalotis, should be normally present in mexicanus. In this 
respect it resembles macrotis of the southeastern United States, but 
otherwise shows no near approach to that species. It is further re- 
markable that the adults are indistinguishable in color from the 
immature individuals, which in other races are darker than the fully 
grown specimens. 
I have provisionally considered all records of Corynorhinus from 
south of Chihuahua as referring to the present race, but the possibility 
that those recorded from Oaxaca or Vera Cruz may be still different 
is not to be overlooked. Through the kindness of Mr. C. D. Bunker 
of the University of Kansas Museum, I have before me a single speci- 
