1 



Some Problems of Freshwater 

 Invertebrate Distribution in the 

 Western States^ 



Robert W. Pennak 



University of Colorado, Boulder 



Any brief discussion of the distribution of 

 free-living freshwater invertebrates of the West (even excluding 

 insects) is a rather large and difBcult matter, chiefly because of the 

 great taxonomic and ecological diversity of the many taxa involved 

 and because of scanty definitive data. For this reason, I shall deal 

 primarily with a few of the basic problems, and I shall limit myself 

 largely to generalizations. My remarks are restricted to the Recent 

 distribution of freshwater invertebrates, other than insects, of the 

 eleven western states. There are six major points which I should 

 like to make. 



1. The freshwater invertebrate fauna of the West is not well 

 known. Aquatic biologists are relatively far more numerous in the 

 eastern half of the United States, where for many years collecting, 

 identification, and zoogeographical studies have been actively 

 pursued. To an even more striking degree, our familiarity with the 

 western freshwater fauna is still farther behind the situation in 

 Europe, where such studies have produced a remarkably thorough 

 knowledge of freshwater invertebrates. 



Our first point, therefore, is a plea for more field, laboratory, 

 and zoogeographical work in our West, especially published work. 

 We hope that, as time goes on, more and more students can be 

 encouraged to enter these fields of research. Incidentally, we suspect 

 that a good deal of unpublished information is already hidden away 

 in field notes, master's theses, and unpublished doctoral disser- 

 tations. 



1 Contribution No. 32, Limnology Laboratory, University of Colorado. 



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