90 



NORTH AMERICAN MUSTELID.E, 



ing any features of eoloratiou that seemed to indicate more than a single 

 American species, or that would serve to distinguish this even from the Mar- 

 tens of the Old World. Dr. J. E. Gray, it is true, had already called atten- 

 tion to the small size of the last molar in the American Martens as compared 

 •with the size of the same tooth in the Old World Martens ; bat, as his obser- 

 vation was apparently based on a single American skull, and as I was at 

 the time strongly impressed with the wide range of individual variation I 

 had found in allied groups, even in dental characters, and also with the great 

 frequency of Dr. Gray's characters failing to be distinctive, I waa misled 

 into supposing all the Martens might belong to a single circumpolar species, 

 with several more or less strongly-marked geographical races. My friend 

 Dr. Coues some months since kindly called my attention to the validity of 

 Dr. Gray's alleged difference in respect to the size and form of the last molar, 

 which I have since had opportunity of testing. This character alone, however, 

 fails to distinguish Mustela foina from AInstela amerkana, in which the last 

 molar is alike, or so nearly so that it fails to furnish distinctive differences. 

 The size and general form of the skull in the two are also the same, the 

 shape of the skull and the form of the last upper molar failing to be diag- 

 nostic. The second lower true molar, however, in Mastda foina presents a 

 character (shared by all the Old World Martens) which serves to distinguish 

 it from Alustehi anlericana, namely, the presence of an inner cusp not found 

 in the latter. In MusteJa flaviguJa, the last molar is relatively smaller than 

 even in Musiela amerkana, and of the same form. Mustela martes differs in 

 its more massive dentition and in the heavier structure of the skull, but 

 especially in the large size of the last molar and the very great development 

 of its inner portion. Hence, while the size and shape of the last upper molar 

 serves to distinguish Ifustela martes from Mustela americana, it fails as a valid 

 distinction between Mustela amerkana and Mustela Jiavigula and Mustela foina. 

 As already remarked, however, Mustela americana lacks the inner cusp of the 

 second lower molar, which is present in the Old World Martens, or at least 

 possesses it only in a very rudimentary condition. 



Miasuremenis of forty -six skulls of Mustela amekicaxa. 



