578 



It differs from Myotis in regard to the dental formula, which agrees 

 with that of the genus Pipistrellus. 



Thus in P. annectens we find characters of two genera combined 

 viz. the dental system of Pipistrellus and in all other respects the cha- 

 racters of Myotis. Consequently a case of transition between forms re- 

 ferred to different genera. 



In the Zootomical Institute I have had an opportunity to examine 

 11 bats, identified as Myotis iiigricans, from different localities in South 

 America: Surinam, Brazil, Argentine and Bolivia. Among those I 

 found individuals in which the second premolar in the upper jaw (pm^) 

 gives an instance of individual variation, being more reduced in size 

 and placed more internal to the tooth-row in one specimen than in the 

 other. 



Among those from Brazil I found a specimen — a female — which 



3 2 



has pm „ — - i. e. the second upper premolar (pm^) of the left side is 



lacking. 



In the same species and from the same locality I found a speci- 



2 2 



men — a male — which has pm - — - (vide fig. 4)i. e. the dental formula 



of the genus Pipistrellus. Between the two premolars there is an inter- 

 space. 



Apart from the dentition it does not differ externally in any way 

 from the other individuals of the same species ; as to its external aspect 

 it is as good a Myotis as any one of the others. The skull does not dif- 

 fer from that of a Myotis, being elevated above the face-line, and not 

 broader or in any remarkable way shorter. The muzzle, the ear, the 

 tragus bear no resemblance to those of a Pipistrellus. The tibiae pre- 

 sent the same proportions as those of Myotis according to the above 

 table. But — as said above — with respect to the coracoid it agrees better 

 with Piyistrelhis than with Myotis^ the coracoid showing a tendency to 

 bifurcation. Thus in this respect and with regard to the dental formula 

 it differs from Myotis and agrees with Pipistrellus. 



The individuals of this species which I have examined, consequently, 

 show a gradual reduction of the second premolar , finally resulting in 

 its total absence. And the last-mentioned individual of Myotis nigri- 

 cans affords one more instance of transition between forms referred to 

 different genera, at the same time indicating one way at least in which 

 those forms originate. 



A similar observation has been made by Allen, wo in a paper ^^ 



11 Gr. M. Allen, Bulletin of the Museum of Comparative Zoology at Harvard 

 College Vol. 52. No. 3. Cambridge, Mass., U. S. A. 1908. p. 45. 



