OCT 1 1R.07 



Article II. — .1 C'oxtriljiitioii to n Kiioiiii'di/c of' Xi>rt]i Amcri- 

 can FresJi-icdtcr Ci/rlop'uhe.* By Ernest B. Forbes. 



INTRODUCTION. 



During the past twenty years the fresh-water Cnjx'jiodd of 

 North America liave received considerable attention from a 

 small number of pioneer investigators, but as yet no one 

 has made a careful comparative study of authentic repre- 

 sentatives of the species described l)y them. It is my pur- 

 pose in this paper to make a first contribution to a revision 

 of the nomenclature of this genus, such as is usually found 

 necessary when, for the first time, the work of unaffiliated 

 investigators is brought into careful comparison. I have 

 embodied in this paper, not a complete revision of the Ameri- 

 can species of Cficlojn^, but only such results of my study on 

 that group as have now been l)rought to a satisfactory con- 

 clusion. 



The excellent work of Claus and Schmeil in Germany has 

 greatly modified our ideas of the comparative value of certain 

 specific characters ; and the revision of the European species 

 of this genus in Schmeil's monograph t has made it possible 

 for me to begin a revision of the American species along the 

 same general lines. 



The r('Ci'pt((ci(liiiii sciniiiis^ which has recently come to be 

 considered as the most important structure for purposes of 

 specific 'distinction, has received almost no attention from 

 American investigators ; but after studying this organ in 

 series of specimens of closely related forms from a great 

 vnriety of widely separated situations, I have been forced to 

 include under the same species name forms which have here- 

 tofore been considered valid species, and to discard as local 

 or at the most varietal difi'erences, distinctions which have 



*This paper was prepared in the course of undergraduate study at the University 

 of niinois. and was accepted by the Faculty of the University June 7, 189T. as a 

 thesis for the degree of Bachelor of Science in Zoology. 



+ Deutschlands freilebende Susswasser-Copepoden, I. Teil: Cyclopidae, 



