120 Nelson Description of a New Species of Lac/omys. 



wash of the upper surface becomes most distinct along the sides 

 bordering the white lower surface, while in collaris it is absent in 

 this region and is most conspicuous on the upper surface of 

 head and back. There also appears to be a higher upward ex- 

 tension of the lower white area along the sides of the latter 

 species. The plain gray of the collar below on the Alaskan 

 animal is replaced on the other species by a band of fulvous or 

 yellowish, which is inclined to spread over the adjoining parts 

 and commonly shades nearly or quite all of the lower surface. 

 There is no sign of this in any of the five specimens of collaris 

 examined by me. The uniform coloration of the upper surface 

 of the head and back, separated by a differently colored collar, is 

 another marked characteristic of collaris. 



Contrasted with L. princeps and L. schisticeps, the most con- 

 spicuous cranial Character of collaris is the much larger size of 

 its audital bullse. They appear to be larger in every dimension 

 than in the other two species. 



The post-palatal notch is broad, as in schisticeps, but the pala-' 

 tine bridge is broad and heavy and slightly concave on both 

 borders. The interorbital width is greater than in schisticeps. 

 The infra-condylar notch of the mandible is more deeply exca- 

 vated than in either of the other species. In addition, the 

 angular process is much more strongly upturned and ends in a 

 sharp point rising vertically behind the concavity of the notch. 

 The horizontal ramus of the mandible is slenderer than in 

 schisticeps and much as in princeps from Idaho. 



To the kindness of Mr. F. W. True, Curator of Mammals in 

 the United States National Museum, I am indebted for the 

 opportunity to examine the material on which the present paper 

 is based. 



Skull metis Lire i nents of three specimens of Lctgomyt collaris from tJie type 

 locality, two hundred miles south of Fort Yukon. 



