172 MICEOTIN^ 



produced into a sj^inous process which juts into the mesoptery- 

 goid fossa. Pterygoid bones usually longer and more slender, 

 the hamular processes less strongly bent outwards than in 

 Syiiaptomys. 



Incisors much weaker relatively ; upper incisors with their 

 grooves less well defined and more centrally situated than in 

 Synaplomys. Mandibular cheek-teeth with crenulate outer 

 borders, lacking closed triangles in consequence of the feeble 

 development of the outer infolds. 



Species and remarks. — The characters separating this sub- 

 genus from true Syiiaptomys although slight are apparently 

 quite definite and constant. Eight species and nine forms of 

 Mictomys are at present recognized, but some of them are of 

 very doubtful validity. Several of the described forms are 

 undoubtedly entitled to systematic recognition ; but it is not 

 improbable that all eventually will have to be regarded as more 

 or less well-marked subspecies of *S'. horcalis Richardson, the 

 earliest and unfortunately one of the least known of the described 

 forms. Richardson's type is in the British Museum, but the 

 skull is in fragments, and until further material is obtained 

 from the neighbourhood of the type locality it will be impossible 

 properly to appreciate the characters of S. borealis. 



Four specimens from Metlakatla, British Columbia, collected 

 and presented by the Rev. J. H. Keen, indicate that the char- 

 acters of m^ and m^, upon which many authors have laid stress 

 when describing sjiecies of Mictomys, are subject to considerable 

 variation in different individuals and in the same individuals 

 at different stages of growth. 



4. Synaptomys (Mictomys) borealis Richardson. 



1828. Arvicola borealis Richardson, Zool. Journ., 3, p. 517; 1829, 

 Fauna Boreali-Americana, p. 127. 



1830. Lemmiis borealis Fischer, Syn. Mamm., p. 585. 



1902. Synaplomys [Mictomys) bnllatus Preble, Proc. Biol. Soc. Wash- 

 ington, 15, p. 181 ; described from Trout Rock, near Fort Rae, 

 Great Slave Lake, Mackenzie, Canada ; type in U.S. Nat. Museum. 



1902. Synaptomys bullata Preble, op. cit., p. 182 ; misprint for bnllatus. 



1907. Synaptomys borealis Osgood, Proc. Biol. Soc. Washington, 20, 

 p. 49. 



TyjK.—^.^l., No. 42.10.7.10; adult in full pelage, taken 

 " in spring after snow had melted " (skin good; skull in frag- 

 ments) ; presented by Sir J. Richardson. 



Type locality.- — Fort J'ranklin, Great Bear Lake, Mackenzie, 

 Canada. 



Range. — ^N.W. Canada between Great Bear Lake and the 

 Rocky Mountains ; southwards as far as Fort Halkett at least. 



Characters. — Size small, hind-foot 14-16 mm. Fur very 

 long and dense, about 22 mm. in length upon the rump. Ears 

 completely hidden by the fur. Colour of upper parts chestnut 



