NO. 1101. PBOCEEDINaS OF THE NATIONAL MUSEUM. 13 



nor the ability or inability of different mammals to hibernate, Never- 

 theless, Dr. Merriam has shown that a relation exists between faunal 

 areas which have been recognized for a long time, and the total amount 

 of heat in those areas, and his theory is therefore deserving of serious 

 consideration. 



A feature in the distribution of the northern genera which merits 

 attention is their failure to cover the entire areas which on theoretical 

 grounds are suitable for them. Why does not Condylura occupy British 

 America generally, the northern Eocky Mountains, etc.? Why does 

 Prt>Y(.s't'rt^o7>s stop in eastern Ohio instead of accompanying Condylura 

 westward to Minnesota? Why <loes not Kenrotrichu-s occupy the 

 mountain ranges of southern California with Scapafius, and why do not 

 these two genera spread out eastward over the northern Rocky 

 Mountains? I appreciate the fact that subsequent researches may show 

 that these genera really do have a more extensive range than is now 

 indicated, but in the present state of knowledge these peculiarities of 

 distribution remain unexplained. It is improbable that in all cases the 

 range will be hereafter shown to be greatly extended. 



As regards Scaloj)^, there is no temperature barrier to prevent its 

 extension across the Plains, and even to the Pacific Coast. That it 

 falls short is evidently due, as already insisted upon, to the condition 

 of the environment as regards humidity. 



DENTITION. 



The formulai for the dentition of the American genera of moles are 

 given by Dobson as follows : 



Coudiilura, i, §; c, |; pm, |; m, |. 

 Scapanus, i, |; c, ■} ; pm, |; m, |. 

 Scalops, i, I; c, ^; pm, §; m, f . 

 Neilrotrichus, i, f ; c, 1; pm, |; m, f . 



In the large series of skulls to which I have had access, are several 

 of each genus sufficiently young to show the milk dentition and the 

 sutures between the various bones. A study of these specimens leads 

 to some rather interesting results. I find that forinuhe based on the 

 position of the suture between the premaxilla and the maxilla deviate 

 in some instances from those given above. If the position of the suture 

 must be rigidly considered in identifying the canine, some formula' now 

 in current use must be abandoned. A similar dilemma seems to have 

 been met with in connection with the European genus TalpUj for Pro- 

 fessor Flower remarks, in Mammals Living and Extinct (p. 23) : 



It happens convenieutly for our purpose that in the great majority of cases the 

 segmentation of the (maxillary) boue coincides with the interspace between the 

 third and fourth tooth of the series; still when it does not happen to do so, as in 

 the case of the mole, we must not give too much weight to this fact, if it contra- 

 venes other reasons for determining the homologies of the teeth. 



! Now, it SO happens that in Scapanus and Farascalops the position 



