6 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



makes it possible to examine vital phenomena directly and watch the 

 effects of stimuli upon the circulation, etc., in continuo. Many curious 

 problems, among them bathymetric distribution and the effects of 

 environment, can be satisfactorily studied in these groups. It is a 

 matter of wonder that greater use is not made of these types in the 

 laboratory courses of our universities. Probably the chief obstacle 

 has been the lack of suitable means of determining species. This we 

 endeavor to offer in so far as may be necessary for this purpose, but 

 purposely abstain from the theoretical questions everywhere pressing 

 on the attention. 



This work claims to be a report on the Crustacea of Minnesota, bufe 

 it was found impracticable to sufficiently describe our forms without 

 a rapid survey of the whole territory. I am under obligations to Pro- 

 fessor C. Dwight Marsh and to Professor E. A. Birge for loan of litera- 

 ture, and to Professor Charles Turner of Atlanta for many notes incor- 

 porated in this work. My greatest obligation is to my ^ife, who has 

 collated the bibliography accompanying. This tedious but most useful 

 labor has been wholly performed by her. 



For many incidental aids during the progress of the work I am 

 indebted to my brother, Professor C. Judson Herrick. 



The reader is requested to remember that this is a revision, follow- 

 ing to a large extent the mould set in 18S4, and therefore should not 

 be held to the standard of a work wholly prepared in the light of our 

 present knowledge. 



The third p.irt of this paper, that dealing with the Ostracoda, is 

 wholly prepared by Professor C. H. Turner, who has been assiduously 

 studying the group for several years, and I feel sure that his contribu- 

 tion will be highly appreciated at the present time, especially as no 

 attempt to monograph the order in America has yet been made. 



Albuquerque. New Mexico, Nov. 1, 1894. 



