A MONOGRAPH OF THE BATS OF NORTH AMERICA. 107 



less rigid tluiu in auy species examined. The tip of the terminal pha- 

 lanx of the fourth digit is minutely lobed and free. 



The dorsum of the interfemoral membrane sparsely covered with 

 silvery tipj)ed hair for four-fifths of its extent; thetibise are involved. 



The wing' membranes are attached to the base of the toes. The fifth 

 metacarpal bone is shorter than the third and fourth, which are of the 

 same length. No raised lines are present in the radio-metacarpal angle 

 or about the muscle-mass at the base of the fifth digit. A delicate 

 raised line is seen on the dorsum of the j)rebrachium. The prebrachium 

 ends at the distal third of the forearm. The distance from the end of 

 the fifth metacarpal bone and the olecranon (the manus being closed) 

 equals one-seventh of the length of the forearm. (In A. f uncus this 

 distance equals one-ninth the length of forearm.) The fourth and 

 fifth metacarpal bones lie well palmed of the third. (In A. fuscus they 

 are on the same line.) In repose the first pluilanx of the third digit is 

 nearly in the same line with the third metacarpal bone, as in N'octilio 

 and Minioptcris. The second phalanx of the same digit is straight. 



In a specimen from Beaverton, Oregon, sent me for examination by 

 Mr. G. S. Miller, jr., Cambridge, Mass., the tip of the calcaral spur is 

 distinctly lobed and the foot is exactly one-fifth the length of tha fore- 

 arm. The membranes and hair are black. 



Variations. — Variation is slight in coloration, notwithstanding the 

 extended range of the species and the great numbers found in certain 

 localities. Leconte describes " entirely black " examples ; these I have 

 never seen. Occasionally the dorsum, where the hair of tlie side of the 

 body ends and that on the membrane begins, is marked by a conspicu- 

 ous line of hair having long white tips. The basal black or brown does 

 not always abruptly end in the tip, but an obscure, rusty-black shade 

 intervenes. I have not met with any varieties with furred thumb. 

 The shafts of the hair in front may be plumbeous instead of brown 

 black. The edges of the lips, as well as the internal basal lobe, are 

 sometimes white. Very rarely the tip of the tragus is pointed instead 

 of blunt. The external basal lobe may extend across the postrictal 

 wart to the mouth. The lobe is very rarely revolute in any degree. 



A specimen from Healdsburg, Cal. (Oal. Acad, of Science), appeared 

 to be somewhat darker, both in fur and membrane, but in essential 

 particulars it was similar to Eastern forms. 



Slull. — There is no trace of a crest at the sagitta; temporal ridges 

 are absent; the mesencephalon equals one-fourth the greatest lengtli 

 of the cranium; the eminence for the i^roencephalon minute and bears 

 two foramina which are near each other ; the vertex of the face with a 

 low nasal eminence for the anterior one-third of the entire region ; the 

 posterior two-thirds is concave; the maxilhe arci deeply concave on 

 either side of the nasal eminence. 



The fronto-maxillary region is produced laterally into a trenchant 

 ridge which causes the inner wall of the orbit to appear concave. The 



