12 NORTH AMERICAX BATS 



Lower Jaw. — Incisors not crowded, bifid. Canine simple, 

 turned markedly ))ack\vard ; basal ridge anteriorl}' well developed ; 

 first premolar larger than the same tooth in Lasiurus, but in com- 

 parison with the second is of itself small. The second premolar, 

 if produced, would not touch an extended line from the canine. 

 The basal ridges of both these teeth are large. Molars proper, 

 not peculiar. 



This genus of Rafincsque's has until recently held an uncertain 

 position. As imperfectly defined by its describer the presence of 

 two incisors only, in the upper jaw, was brought out as the pro- 

 minent generic characteristic. But, as it was afterwards observed, 

 the incisors are va.rial)le, the young, it was thought, having four 

 incisors, the adult but two. And even this observation applied 

 more to the genus as then understood than to it as now restricted ; 

 for the above fact in relation to the dentition is also observed in 

 L. noveboracensis. So we conclude that the presence of but two 

 incisors in the upper jaw of Nycticejus is still a permanent 

 character, though not a very important cue. 



IVycticejiis crepuscularis, Allen. 

 Fig. 10. Fig. 11. 



Vesperiilin crepuscularis, Lec, Cuv. An. Kingdom (McMurtriQ ed.), I, 



1831, 432.— Ib., Proc. Acad. Nat. Sci. VII, 1855, 433. 

 Vespertilio creeks, Fr. Cuv. Nouv. Ann. du Mus. I, 1832, 18. 

 Nycticejus humeralis, (?) Raf., Journal de Physique, LXXXVIII, 1819, 417. 



Description. — Ears small, internal basal lobe small and curved; 

 the external basal lobe also rather inconspicuous ; between the 



