The Lemmings of the Genus Synaptomys. 57 



tomys innuitus The characters that separate it from Synaptomys 

 proper seem of subgeneric rather than generic weight, and in the 

 present paper Mictomys is treated as a subgenus of Synaptomys. 



In 1874,' 2 and again in 1877, 3 Coues referred to Synaptomys 

 cooperi, a specimen from Skagit valley, Washington, collected in 

 1859 by C. B. Kennerly, and one from Nulato, Alaska, collected 

 in 1867 by William H. Dall. These specimens are still in the 

 U. S. National Museum, and through the courtesy of Mr. True 

 I have been enabled to compare them with his type of Mictomys 

 innuitus, which they closely resemble. Both belong to the sub- 

 genus Mictomys, but differ sufficiently from innuitus and from 

 each other to warrant separation. They are here described under 

 the names truei and datli. 



In September, 1895, Clark P. Streator collected, at Wrangel, 

 Alaska, still another member of the same group, which is here 

 named wrangeli. 



Summary. The material now available shows that the genus 

 Synaptomys, instead of being monotypic, as until recently sup 

 posed, comprises 2 well marked subgeneric groups Synaptomys 

 proper and Mictomys ; that Synaptomys proper inhabits eastern 

 Canada and the northeastern United States from Minnesota to 

 New Brunswick and New England, and contains 4 fairly well 

 denned forms ; that Mictomys has a transcontinental distribution 

 from Labrador to Alaska, and contains at least 4 species. 



Synaptomys, like the other genera of lemmings, is a distinctly 

 boreal group. Of the two subgenera, Mictomys is decidedly the 

 more boreal, being strictly confined, in the east at least, to the 

 Hudsonian zone. The subgenus Synaptomys pushes southward 

 to the northern edge of the Austroriparian zone, but after it leaves 

 the Boreal zone it occurs only, so far as known, in cool swamps. 



Genus SYNAPTOMYS Baird. 



Subgenus St/naptomys Baird, 1857. 



Inferior molars with well denned closed enamel loops on outer side ; 



upper incisors very broad and heavy, with enamel face deep 



orange throughout ; posterior end of palate without median 



azygos ridge or projection. 

 Subgenus Mictomys True, 1894. 



Inferior molars with 110 closed 



enamel loops on outer side ; 



upper incisors relatively 



narrow and weak, with en 

 amel face pale yellow and 



part on outer side of sulcus 



nearly white ; posterior end 



of palate with a strongly 



marked median azygOS FIG. i. Enamel pattern of lower molars, 

 ridge and projection. T_. Synaptomys 2. Mictomys, 



