AMERICAN BATS OF THE GENERA MYOTIS AND PIZONYX 33 



sequently not been able to find any recognizably different general 

 totals of specialization for the members of the group as compared 

 with one another, or any main line of modification along which the 

 evolution of the American species has progressed. Since a linear 

 arrangement which would represent a natural sequence is thus clearly 

 out of the question, for the present at least, the order of enumeration 

 which we have chosen is in the main an arbitrary one. It begins with 

 the longest-known and most wide-ranging American species, Myotis 

 ludfugus^ as a fairly generalized representative of the genus. The 

 other large-footed species follow, then those with small foot and 

 keeled calcar. Finally we have found it convenient to give separate 

 treatment to the tropical and South American members of the genus. 

 There is practically no overlapping of the ranges of these and of the 

 forms which occur in temperate North America; furthermore they 

 are much less completely known. 



Genus PIZONYX Miller 



Pizomjx Miller, Proc. Biol. Soc. Washington, vol. 19, p. 85, June 4, 1906; 

 Fam. and Gen. Bats, Bull. U. S. Nat. Mus., No. 57, p. 202, June 29, 1907; 

 List North Amer. Land Mamm. 1911, Bull. U. S. Nat. Mus., No. 79, p. 59, 

 December 31, 1912. — Elliot, Check-List Mamm. North Amer., suppl., p. 157, 

 1917.— MiLLEB, List Recent Mamm. North Amer. 1923, Bull. U. S. Nat. Mus., 

 No. 128, p. 73, April 29, 1924. 



Gciivotype. — Myotis vivesi Menegaux. 



C hctracters. — Like Myotis but foot so enlarged that, with the claws, 

 it about equals the length of the tibia ; toes and claws so greatly com- 

 pressed that the width of claw is only about one-eighth the height of 

 the claw at base; wing membrane abruptly narrowed in region of 

 knee ; a large glandular mass in wing membrane near middle of fore- 

 arm; teeth showing a general tendency to heightening of cusps; sec- 

 ond premolar, both above and below, larger than first. 



Distribution. — Islands and coast of the Gulf of California, Mexico. 



Remarks. — The genus Plzonyx, though nearly related to Myotis, 

 is well differentiated by the remarkable development of the foot, and 

 by the other characters which have just been mentioned. In size and 

 general appearance, apart from the enlarged feet, the single known 

 species of Pizonyx bears a resemblance to Myotis myotis of the 

 palearctic region. This resmblance is, however, purely superficial. 

 That Pizonyx can not have been derived from some member of the 

 Myotis myotis group is shown by its retaining the normally developed 

 7)}?., whereas a reduction of this tooth is one of the main character- 

 istics of M. m^yotis and its allies (see p. 10). 



