No. 13. — The American Collared Lemmings (Dicrostonyx). 

 By Glover M. Allen. 



Introduction. 



The Collared Lemmings of the genus Dicrostonyx are circumboreal 

 in distribution and highly characteristic of Arctic lands. In the 

 Old World, they inhabit Spitzbergen, Nova Zembla, and the Asiatic 

 continent bordering the Arctic Ocean, but in comparatively recent 

 geological times (late Pleistocene) they were present in Great Britain 

 and on the European continent as far south at least as Belgium, 

 central France, and Germany, evidently forced southward by the 

 encroaching ice-cap during the last period of glaciation. Associated 

 with the fossil remains of Dicrostonyx in Europe, are those of rein- 

 deer, musk ox, the Common Lemming (Lemmus), and other tundra- 

 loA'ing species characteristic of Arctic and Subarctic country. With 

 the return of a warmer climate, this barren-ground fauna has retreated 

 northward so that at the present time the Collared Lemming is no 

 longer found in Europe, though it reaches western Siberia in the Obi 

 region. Of the former distribution of the genus in Asia and in the 

 New World, no positive evidence has as yet been discovered. No 

 doubt, however, it was driven southward at the same time that the 

 ice-sheet overspread Europe and northern America, and it may have 

 lived with the musk ox and reindeer, the fossil remains of which are 

 found in the central states. 



The present distribution of Dicrostonyx in America is suggestive 

 of Postglacial change. Two types now occur; a more primitive 

 confined to the Labrador Peninsula; and a more evolved, similar 

 to the fossil and living Asiatic type, the range of which includes 

 western Arctic America, west of Hudson Bay, the Arctic Archipelago, 

 and the north coast of Greenland. Associated with this type in 

 continental Asia and in x\merica west of Hudson Bay is the genus 

 Lemmus, or typical Lemming, also of x\rctic and Subarctic distribu- 

 tion. The isolation of the Labrador Lemming and the absence 

 from that peninsula of the boreal genus Lemmus, suggest that the 

 Labrador animal is a relict that still persists there, having followed 

 the ice-sheet in its retreat northward. The concomitant advance of 

 the forest to James Bay effectually cut off its range from invasion by 



