North American Fresh-ivater Cyclopidce. 57 



Ordinarily the egg-sac tapers to a sharp point at the lower 

 end, and stands out from the abdomen at a wide angle. 



The size is remarkably variable. In Europe, the length 

 varies from .883 to 2.2 mm. In America I have measured 

 specimens varying in length from .54 to 1.47 mm. A com- 

 mon length is .9 mm. 



Cyclops prasinus Fischer. (PI. XIX., Fig. 1 and 2, and 



PI. XX., Fig. 1 and 2.) 



Cyclops pr a stmts, Fischer, '(iO. pp. C52-654. PI. XX., Fig. 19-26a. 

 Cyclops fliiviatllis, Ilerrick, '82 a. p. 231, PI. VI I.. Fig. 1-9. 

 Cyclops magnoctavus, Cragin, "83, pp. 70.71, PI. III.. Fig. 14-23. 

 Cyc/ups prasinus, Schmeil, '92. pp. 150-15G. Pi. V., Fig, ]-5. 

 t )/c lops fluviatilis, Ilerrick and Turner. '95, pp. 114. 115, PJ. XXVI., 

 Fig. 1-8; XXX., Fig. 1. 



SYNONYMY AND DISTRIBUTION. 



On account of the great difficulty in determining the struc- 

 ture of the receptaculum seminis of C. prasinus, this organ 

 has escaped study in the American representatives of this 

 species, and although Marsh had noted a general resemblance 

 of Herrick's C. fluviatilis to Yosseler's ('. pentagonus (C. 

 prasinus Fischer), he did not consider these as identical. By 

 a careful study of a large number of specimens of C. fluviat- 

 ilis from Illinois, Florida, and Wisconsin, I find a complete 

 agreement in the characters of the receptaculum seminis of C. 

 prasinus and C. fluviatilis and in all other specific characters 

 as well. 



I have noted the occurrence of ('. prasinus in collections 

 from Sister Lake, Florida ; Long Lake, Adams county, 111. ; 

 ponds and temporary pools at Urbana, 111. ; Illinois Piiver at 

 Havana, 111. ; Phelps, Flag, and Thompson's lakes in Ful- 

 ton county, 111. ; Dogfish and Quiver lakes in Mason county, 

 111. ; and from Lake Geneva, Wisconsin. Ilerrick reports it 

 from Lake Minnetonka, Minn., and from an estuary of the 

 Mississippi. Marsh finds the species in Lakes Erie, Michi- 

 gan, and St. Clair, and in fifteen smaller lakes of Michigan 

 and Wisconsin. Cragin found it in ditches at Cambridge, 

 Mass. 



