A MONOGRAPH OF THE 13 ATS OF NORTH AMERICA. 47 



above, and uiiicoloied save at the ti[)S, which is distinctly cinerous. 

 The tleshy part ot" the forearm was covered with haii', wliich was di- 

 rected toward the elbow. The dorsal surface of the first metacarpal 

 bone was marked with a small clump of hair. 



In two specimens collected by the expedition of the Philadelphia 

 Academy of Xatural Sciences at IJxmal, Yucatan, in 188!), the <;'cneral 

 a])pearance of the venter was mouse- gray beneath, with silvery tips to 

 the hair, and that of the dorsum was darker and without gray, except 

 the two faint stripes on the head. The head and neck were for the 

 greater part white, the tip alone being ash gray. The white lines on 

 the head were inconspicuous. On the side of the neck the hair was of 

 the above type, but much longer. The front of the neck was nearly 

 unicolored, the basal one-tifth alone being white. The dorsum was dark 

 lustrous and uncolored at the loin. The venter was provided with dis- 

 tinctly ashy appearance of the tips, but the rest of the fur was ash 

 brown. 



Membranes. — The prebrachium with free margin occupied with a baud 

 1""" wide, which apparently represents the tendon of the occipito-pollicis 

 muscle; intercostal markings conspicuous, four in number; the lowest is 

 the largest and extends as far as the ankle. The oblique line, which 

 passes upward and outward as far as the ankle on the mesopatagium 

 in many genera, is here absent. The line of the fascicle of the coraco- 

 brachialis is conspicuous and extends to a x)oint in a vertical line with the 

 elbow. The lines of the vertical platysma fascicles are about thirty in 

 number. The system into which the triceps-fascicle enters extends as far 

 as the end of the tifth digit. It is composed of three divisions, a vertical, 

 obi ique, and a horizontal. The fourth interspace is provided with a faintly 

 marked longitudinal line, which begins at a point 22'""' from carpus and 

 extends to a point 10""" from the free margin of the membrane. The pre- 

 digital nerve appears at the middle of the fifth metacarpal bone, and is 

 larger than the post digital, which appears at the metacarpo phalangeal 

 joint of the third finger. The third interspace is also ])rovide(l with 

 a longitudiiuil line. It extends from near the i)alm and reaches to 

 within 10""" of the free nuirgin of the membrane. A nerve appears at 

 the metacarpo-phalangeal joint of tiie fourth finger and lies obliquely 

 across the lower part of the interspace. The fourth phalanx of the third 

 digit is sickle shaped, the membrane being to its tip; that of the fourth 

 digit is of the shape of an inverted T; that of the fifth is triangular, 

 the angle, which is directed toward the body, being prolonged. 



Skull. — The skull is massive, broad, as compared with other crania iu 

 the order. Concave muscular impressions are defined in the region 

 directly back of the temi)oral bone. The mastoid ])rocess is longer than 

 the paroccipital. The tympanic bone is complete above, tliough the 

 suture between the two i)arts is conspicuous. The bone is small as 

 compared with the same part in other genera: it recedes sliglitly from 

 the free border of the squama, and as seen from below leaves the cochlea 



