54 Illinois State Laboratory of Natural History. 



Subgenus Eucyclops Claus. 

 Cyclops serrulatus Fischer. (PI. XVII., and PI. XVIII., 

 Fig. 1-3.) 

 Cyclops serrulatus and (J. serrulatus var. montanus, Brady. '78, Vol. 



I., pp. 109-111, PI. XXII., Fig. 1-14. 

 Cyclops serrulatus and C. serrulatus var. elegans, Merrick, '81, PI. <,». 



Fig. 17-19; PI. Q ; . Fig. 10. 

 Cyclops serrulatus, Schmeil. '92, pp. 141-14U, PJ. V.. Fig. 0-14. 



SYNONYMY, VARIATION, AND DISTRIBUTION. 



This is one of the most common and widely distributed of 

 American ( 'yclops. It occurs almost everywhere between 

 Maine and California and from Florida to Manitoba. 



Herrick's variety elegans is based on such variable charac- 

 ters that no one acquainted with the species throughout its 

 range could for an instant consider this form as worthy of a 

 varietal name, especially since the measurements and descrip- 

 tions of the type and the variety are contradictory as pub- 

 lished in his "Synopsis of the Entomostraca of Minnesota." 

 Herrick says that the variety is distinguished from the type 

 by its greater size and by the elongation of the antennae and 

 caudal stylets; but gives 1.5 mm. as the length of the type, 

 and 1.34 as that of the larger variety. In Europe the largest 

 specimen on record measured 2.2 mm. in length, much more 

 than Herrick's large variety. As to the length of the antennae, 

 I find that this varies immensely and quite independently 

 of other variations in proportion. Below is a series of meas- 

 urements of seven egg-bearing females of this species, from 

 widely separated situations and exhibiting its variability. 

 Further study of a much larger number of specimens has 

 convinced me that there are no varietal distinctions possible 

 among the American representatives of this species, unless 

 for convenience we arbitrarily separate off the extreme forms. 

 With the exception of the specimen from Thompson's Lake, 

 each individual is fairly representative of the species as found 

 in its own locality. 



