106 



liEVISIOX OF AMERICAN MOLES— TRUE. 



The lower milk Incisors are absent. The canine is small and unicus- 

 pidate. The first premolar is two-rooted and about as large as the 

 permanent one and probably of similar shape, but it is considerably 

 ■worn down so that its original form can not be made out. The same is 



true of the second milk premolar, which is 

 two-rooted and as large as its successor.' 



HISTORY OF THE SPECIES. 



The history of Gibbs's mole is very sim- 

 ple. The species was first described by 

 l*rofessor Baird, in 18.")7,^ from a young- 

 specimen obtained by Dr. Suckley in the 

 White River Pass, Washington. It was 

 idaced in the Japanese genus Urotrichits, 

 to wliich it bears a very close external resemblance. In 1880 Dr. 

 Giinther called attention to the differences in dentition, and estab- 

 lisliod the genus Xenrotrichns for the American form.^ Since that 

 date no changes have been made in the status of the form, but prob- 

 ably from lack of specimens in European museums the validity of Dr. 

 (liinther's genns has not been so generally recognized as it deserves 

 to be. 



Dimensions of skulls of Neiirotrichiia gihbsii. 



4G. 



JAWS OF TYPE OF NEfROTKIfHr.' 

 GIBBSII. 



(•}*^ limes nritiiral size.) 



' The skull from Crescent City, California, retains the nppor milk canine behind the 

 permanent one on each side. 

 -Rept. racific R. R. Survey, VIII, 1857, p. 7(i. y\. \x\ 111. 

 sProc. Zool. Soc, 1880, p. 441, pi. XLii. 



