178 University of California Publications in Zoology [Vol. 24 



shows the manner in which ratio of length of tail to total length acts 

 between one extreme and the other. There is a gradual lengthening of 

 tail as the lower river is approached. On these grounds I believe that 

 macrurus should be treated as a subspecies of Microtus mordax. Mic- 

 rotus mordax mordax may be regarded as occurring along the Stikine 

 River at least as far down as a point (Clearwater Creek) some twenty- 

 miles from the mouth of the river. 



Microtus vellerosus was described by Allen (1899, p. 7) from the 

 Liard River, and specimens from Telegraph Creek were referred by the 

 same writer (1903, p. 548) to that form, regarded as a subspecies, 

 Microtus mordax vellerosus. Bailey, in his revision of the genus 

 Microtus (1900, p. 48, footnote) , denies recognition to this race, regard- 

 ing it as inseparable from typical Microtus mordax mordax. Compar- 

 ing our Telegraph Creek specimens with series of mordax from north- 

 ern California, I am unable to distinguish between them, consequently 

 I follow Bailey in the use of the name mordax for the northern animal. 



TABLE III 



Measurements in millimeters (average, minimum and maximum) of adult Microtus 

 from the Stikine region and from southeastern Alaska 



Microtus mordax mordax Total length Tail vertebrae Hind toot 



10 adults, The Junction, 



Stikine River 170.6 (155.0-180.0) 55.3 (50.0-62.0) 20.9 (20.0-22.0) 



10 adults, Telegraph Creek, 



Stikine River 182.5 (170.0-197.0) 60.8 (51.0-70.0) 21.0 (20.0-22.0) 



10 adults, Glenora, Stikine 



River 192.2 (HO.0-206.0) 66.7 (52.0-76.0) 21.4 (21.0-22.0) 



8 adults, Doch-da-on Creek, 



Stikine River 184.1 (170.0-200.0) 62.9 (55.0-70.0) 21.0 (20.0-22.0) 



7 adults. Flood Glacier, 



Stikine River 186.4 (180.0-200.0) 66.1 (62.0-70.0) 22.4 (22.0-23.0) 



Microtus mordax macrurus 



5 adults, Mitkof Island, 



s.e. Alaska 174.2 (164.0-183.0) 70.4 (68.0-72.0) 21.8 (21.0-22.0) 



10 adults, Prince of Wales 



Island, s. e. Alaska 189.3 (172.0-207.0) 73.3 (63.0-80.0) 21.1 (20.0-22.0) 



