AMERICAISr BATS OF THE GENEEA MYOTIS AND PIZONYX 211 



Wing and meriihranes. — Metacarpals conspicuously graduated by 

 steps of about 5 mm., the fourth approximately equal to the forearm, 

 and the third about 3 mm. longer. Wing membrane narrowed in a 

 peculiar mafnner, so that when the wing is half extended the margin 

 of the membrane behind the elbow extends in an approximately 

 straight line from the tip of the fifth digit to the region about 15 

 mm. out from the knee ; then it bends backward, rapidly approaching 

 the tibia and finally arriving at its point of insertion on the dorsal 

 surface of the outer side of the metatarsus. The result of this narrow- 

 ing is that the lower leg is practically freed from the wing membrane, 

 a condition strongly contrasted with that present in all the American 

 species of Myotis (and in the large palearctic My oils miyotis), in 

 which the border of the membrane in the half-flexed wing extends as 

 a straight line from the fifth finger to the ankle or foot. The end 

 of the tail projects beyond the general outline of the free border of 

 the uropatagium, but a narroAv margin of membrane extends prac- 

 tically to the extreme tip. 



Foot. — The foot is remarkable for its very large size. In adults 

 the claws can almost be hooked over the knee, while in half-grown 

 individuals they extend considerably beyond the knee when the ankle 

 is strongly flexed. The enlargement is not due to a uniform length- 

 ening of all the elements of the foot, but to changes which chiefly 

 involve the phalanges and claws. In an ordinary large-footed 

 Myotis such as M. thysanodes the metatarsus is more than half as 

 long as the combined phalanges and claws; in Pizonyx vivesi it is 

 barely one third of this length. The lateral compression of the 

 digits and claws seen in all species of Myotis is here carried to an 

 extreme development. A few very fine hairs scattered over the sur- 

 face of the foot can be detected with the aid of a lens. Calcar deep- 

 ened and laterally compressed at its base, the area of its attachment 

 to the heel assuming almost the character of a definite joint. Its 

 length is about equal to that of the foot or tibia. It terminates in- 

 distinctly and bears no keel. 



Fur and color. — The fur shows no special peculiarities. Longer 

 hairs at middle of back about 8 mm. in length. It does not definitely 

 extend out on any of the membranes. Uropatagium practically 

 naked below except for a sprinkling of long loose hairs at its base 

 and near the legs and a fine pubescence of minute silvery or yellowish 

 brown hairs on its distal third; the upper surface has the same 

 loosely sprinlded basal area and bare median region, but the distal 

 third bears a thick growth of appressed backwardly directed hairs 

 3 to 5 mm. in length which form an almost furry coating. Color 

 above nearly the wood brown or fawn color of Ridgway (1912), the 

 hairs slaty at base; underparts whitish in strong contrast with the 



