AMERICAN BATS OF THE GENERA MYOTIS AND PIZONYX 9 



lucifugus, but the protoconule is absent and the paraloph may 

 extend from the base of the paracone well up toward the summit of 

 the protocone. 



In the third upper molar the process of reduction seems to be 

 concentrated on the posterior segment of the tooth. The anterior 

 portion in Myotis lucifugus (fig. la) remains essentially as in the 

 first and second teeth. The metastyle is, however, completely sup- 

 pressed, and the loph extending to it from the metacone is reduced 

 to a mere trace running downward and directly backward along the 

 posterior surface of the metacone. The metaloph has also disap- 

 peared; but the hypocone is still visible as a minute remnant. Ex- 

 treme reduction (fig. 16) takes the form of still greater antero- 

 posterior shortening of the crown, together with the complete and 

 final elimination of the metaconule and its loph as well as the hypo- 

 cone. In this stage, however, the protoconule usually persists, even 

 when it has completely disappeared from ni^ and ?;r. This condi- 

 tion is best shown by Myotis w,yotis, the species figured, but it is 

 approached in the American M. thysanodes and M. evotis. 



The crowns of the upper molars bear no cingulum on the outer 

 side, but the lingual and hinder borders are margined by a cingulum 

 which, beginning at about the level of the protoconule on the anterior 

 side, extends around the lingual border and out along the posterior 

 margin to the metastyle. This cingulum is subject to much varia- 

 tion in development. Usually its continuity is nearly or quite broken 

 at the antero-lingual portion of the base of the protocone. Less often 

 there is a break at the postero-lingual bulge of the base of the hypo- 

 cone. In rare instances the cingulum may be reduced, along the 

 entire lingual border of the crown, to a series of irregularly devel- 

 oped enamel nodules. Still more rarely it may bear an incipient 

 cusp in the region of the hypocone. As is the case with the secondary 

 cusps the cingulum shows a more reduced condition in the type 

 species of the genus, Myotis myotis, than it does in any of the known 

 American forms. 



Were the extreme types of cusp development isolated they might 

 well be considered as furnishing characters of generic or subgeneric 

 importance, but so many intermediate conditions occur that it seems 

 impossible to attribute any such weight to these structures. Ap- 

 parently the more complicated type is the one which is to be re- 

 garded as representing the condition primitive for the genus Myotis. 

 It occurs in all the American species except M. evotis and M. thy- 

 sanodes. Among the Old World forms we have found it in speci- 

 mens determined, with varying degrees of authenticity, as adversus, 

 hocagei, capaocinii, ca7%7nonensis, dasycneme, daubentonii., hilde- 

 gardcB, 'macrotarsus, and irvwrcMs. A more simplified structure re- 

 58518—28 2 



