DISTKIBUTION AND KEY OF THE XORTH AMERICAN 

 COPEPODS OF THE GENUS DIAPTOMUS, WITH THE 

 DESCRIPTION OF A NEW SPECIES 



By C. DwiGHT Marsh 



Of the United States Department of Agriculture 



Since the publication of the " Revision of the North American 

 Species of Diaptomus " in the Transactions of the Wisconsin Acad- 

 emy of Sciences, Arts, and Letters b}' Marsh in 1907, there have been 

 many collections of material containing Diaptomi in various parts of 

 North America and quite a number of publications have been issued 

 by several investigators. There has been no other publication cover- 

 ing the genus as a whole except the synopsis by Marsh in Ward and 

 Whipple's Fresh-Water Biology, and ToUinger's paper on distribu- 

 tion published in 1911. 



In addition to the published material, the author has accumulated 

 many data from collections belonging to the ITnitecl States National 

 Museum, and others which have been sent to him, and from numerous 

 collections made by him personally. It is thought that a paper 

 covering the present knowledge of the distribution of the species 

 would be helpful to others. 



It is understood, of course, that such a paper gives only the known 

 distribution. In spite of the considerable number of collectors, only 

 limited portions of the country have been studied with anything like 

 thoroughness. Most of the collections have been of a sporadic char- 

 acter, sometimes in only one or two localities in a State; very few 

 collections have been made in the whole region of Canada, and Mex- 

 ico is almost an unknown territory. Wliile it can ordinarily be 

 assumed that a species is found in the regions intervening between 

 its extreme limits, it can not now be known what the extreme limits 

 are, so that it is probable that the distribution is much wider than is 

 shown by the collections. In the charts, in nearly all cases, the 

 actual places of collections are indicated rather than a region where 

 the species may be found. Perhaps all the locations for such species 

 as D. oregonensis and D. minutus are not indicated in Wisconsin 



No. 2785.— Proceedings U. S. National Museum, Vol. 75, Art. 14 



330T3 — 29 — — 1 1 



