8 



BULLETIN 144, UNITED STATES NATIONAL MUSEUM 



which disappears. An anomaly which has been twice observed (in 

 M. thysanodes No. 52228, U. S. N. M., and M. lucifugus carissima 

 No. 38029, U. S. N. M.) consists in the coalescence of the two small 

 teeth on one side of the upper jaw; and in one instance (see p. 53) 

 we have found a third small tooth welded to the anterior margin of 

 the large premolar. 



The upper molars present some important structural peculiarities 

 which should be carefully understood. 



In the first and second of these teeth the most complicated type 

 of cusp development is the one which is found fully displayed in 

 Myotis lucifugus (fig. Ic). In this type the hypocone is a large 

 and obvious element of the crown plan, its base well indicated as a 



swelling distinct from that 

 which forms the base of 

 the protocone, its point 

 sometimes but not always 

 standing out from the high 

 longitudinal loph which 

 connects the summit of the 

 protocone with that of the 

 less elevated hypocone. A 

 noticeable metaloph extends 

 from the base of the meta- 

 cone across the deep valley 

 which lies between the meta- 

 cone and hypocone. This 

 ridge passes up the inner 

 side of the hypocone to the 

 longitudinal loph (as in the figure) or in some instances to the 

 actual summit of the hypocone itself. On the anterior margin 

 of the crown a conspicuous triangular protoconule lies in the space 

 between the protocone and paracone. This small cusp is connected 

 with the base of the paracone by a short but very obvious ridge 

 which may be spoken of as the paraloph. The opposite extreme, 

 so far as the American members of the genus is concerned, is seen 

 in Myotis thysanodes (fig. le). Here the inner side of the tooth 

 is somewhat narrowed, chiefly at the expense of the hypocone; 

 the metaloph, protoconule, and paraloph have completely disap- 

 peared, leaving a deep smooth-floored valley between the hypocone 

 and metacone and another between the protocone and paracone. In 

 the type of the genus, the palearctic Myotis myotis^ this reduction 

 process is carried so far that the hypocone is normally smaller than in 

 M. thysanodes, and in some individuals it practically does not exist 

 as an element distinguishable from the base of the protocone. A 

 peculiar condition is sometimes seen in the genus Pizonyx (fig. Id), 

 Here the hypocone and metaloph are essentially as in Myotis 



Fig. 1. MOLAK TKETH OF MYOTIS AND PiZONYX : a, 



ms of Myotis lucifugus ; &, m^ of Myotis 

 myotis ; c, m 2 of myotis lucifugus ; d, m = 



OF Pizonyx vivesi ; e, m= of Myotis thy- 

 sanodes. All gkkatly bnlabged, not to scale 



