North American Fresh-water Cyclopidce. 45 



pond at Wood's HolJ, Mass. The most conspicuous difference 

 between this form and C. thomasi is a slight one in the shape 

 of the fifth foot. 



In the Illinois River are specimens which bridge over com- 

 pletely the gap between C. bicuspidatus and Herrick's C. 

 navus, and I see no reason for considering navus as a good 

 variety. 



Cyclops minnilus Forbes is distinguished from C. thomasi 

 by different proportions alone. It is one of the western rep- 

 resentatives of this species and has been collected in the 

 lakes and rivers of Wyoming. 



Cyclops serratus Forbes is found in the same situations as 

 C. minnilus, from which it is distinguished by a slight differ- 

 ence in the armature of the feet and by the fact that the 

 vertical comb of spines of the furcal stylets is but poorly 

 developed. The name xerrtrfiiH being already in use, Herrick 

 renamed the species forbesi. This is the most elongate of 

 the American representatives of the species. 



SPECIFIC DESCRIPTION. 



This is a long and slender species (PI. XII., Fig. 1) with 

 seventeen-segmented antennae, oval cephalothorax, slender 

 abdomen, very long and slender caudal stylets, and but two 

 developed seta; to each stylet. The longer of these setaa is 

 about twice as long as the shorter. The cephalothorax is 

 widest at about the middle. In specimens from the eastern 

 United States the posterior angles of the cephalothorax are 

 not usually prominent except in the case of the last segment, 

 where they are laterally produced. In the far western speci- 

 mens the posterior angles of all the segments are prominent. 

 The peculiar appearance of the cuticle caused by circular pits 

 or depressions which Dr. Schmeil mentions, is rarely present 

 in the iVmerican form. I have found it in greatly varying 

 degrees of definiteness in specimens from Lake Superior 

 and from Wyoming. 



The first segment of the abdomen of the female (PI. XII., 

 Fig. 1) is emarginate behind the prominent lateral angle. 

 This segment is about as long as all the others together. The 



