North American Fresh-water Cyclopidce. 31 



the specimens have been killed in alcohol ; but this difficulty 

 is readily avoided by the use of formalin as a preservative. 

 A 1% solution is amply strong, and the osmosis of fluids is 

 not rapid enough to rupture the receptaculum, as is the case 

 when strong alcohol is used. Some slight differences in the 

 appearance of the receptaculum are due to stage of sexual 

 activity of the animal. In the case of C. viridis var. insectus 

 such a difference is noticeable. In Fig. 3, PL XL, the solid 

 line represents the outline of the empty receptaculum ; the 

 dotted line, the shape when fully distended. 



Through the generosity of Prof. G. 0. Sars and Dr. Otto 

 Schmeil, I have received much valuable material from Europe, 

 by means of which I have been able to compare American and 

 European forms. I wish also to acknowledge the assistance 

 received from my co-laborers, Messrs. Pi. W. Sharpe and F. 

 W. Schacht, and also to thank Prof. L. S. Eoss, of Drake 

 University, and Mr. Adolph Hempel, now of the Museu 

 Paulista, Brazil, for the courtesies shown me in the loan 

 and collection of material. A very great part of the credit 

 for such portions of this paper as may be of value is due to 

 my instructor, Dr. S. A. Forbes, whose kind supervision and 

 encouragement have constantly guided and aided me in this 

 work. 



Genus Cyclops 0. F. Muller. 

 Subgenus Cyclops s. str. Glaus. 

 Cyclops leuckarti Claus. (PL VIII., Fig. 1-3.) 



Cyclops leuckarti, Claus, '57, p. 35, PI. I., Fig. 4; PJ. II., Fig. 13, 14. 

 Cyclops leuckarti, Schmeil. "92, pp. 57-64, PI. III., Fig. 1-8. 

 Cyclops leuckarti, Herrick and Turner, '95, pp. 90-98, PI. XVI.; 

 XVIII., Fig. 1, A-J: XXIV., Fig. 2-0. 



This species is of medium size, but is rather more slender 

 than usual (PL VIII., Fig. 1). The cephalothorax is broadest 

 at the first segment and tapers conspicuously toward the 

 posterior end. The length as compared to the breadth is 

 about as eleven to six. 



The abdomen is long and slender, but the stylets are short, 

 being one third or one fourth as broad as long. They are 



