Article II. — A Contribution to a Knowledge of North Ameri- 

 can Fresh-water Cyclopia" ce.* By Ernest B. Forbes. 



INTRODUCTION. 



During the past twenty years the fresh-water Copepoda of 

 North America have 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 by 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 Cyclops, but only such results of my study on 

 that group as have now been brought to a satisfactory eon- 

 elusion. 



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! has made it possible 

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

 same general lines. 



The receptaculum seminis, 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 

 variety 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 differences, distinctions which have 



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

 of Illinois, and was accepted by the Faculty of the University June 7. 189", as a 

 thesis for the degree of Bachelor of Science in Zoology. 



HDeutschlands freilebende Siisswasser-Copepoden, I. Teil: Cyclopidae. 



