North American Fresli-watcr Cyclopid<e. 43 



Pond, Normal, 111 G3 : 9 



Creek. Wyoming. .... 52:11 



Lake AVinncbago. . . 52:8 



Lake Superior, . . . 44:9 



Illinois River 40:9 



Mississippi River. . . . 37:8 



Pond, Urbana, 111 34:7 



Pond. Yellowstone Park, . . 33:9 



Slough, Manitoba, . . . 33:9 



There is a very peculiar semicircular indentation of the 

 outer side of the basal segment of the inner ramus of the 

 fourth foot often present in this variety, hut it may he 

 entirely absent or only present in a slight degree of develop- 

 ment. Whatever the function of this peculiar indentation, it 

 does not seem to be essential to the animal. 



The fifth foot varies but little in the basal segment but the 

 distal segment is peculiarly variable. In one extreme, which 

 reaches its highest development in the Illinois River, this seg- 

 ment is very short, its length compared to its breadth being 

 as 3.5 to 3, and its sides strongly outcurved. The small 

 spine is situated some distance from the end of the segment 

 and is very small indeed. Examples of the other extreme 

 are common in the ponds of central Illinois. In these the 

 last segment is much longer, its length being to its breadth 

 as 9 to 5. In this form the spine is parallel to and often 

 longer than the segment. 



The shape of this distal segment seems to vary independ- 

 ently of the other specific characters, and all gradations 

 between the two forms may be found in a single pond. These 

 variations are not demonstrably connected with the environ- 

 ment. 



The receptarnlioii soniuis (PI. XI., Fig. 3) is, when fully 

 distended, of the shape represented by the dotted line, but 

 otherwise may have the shape outlined b> the solid line. As 

 will be seen by comparing this figure with that of the rcccp- 

 tdciilidit scntiiiis of ('. riridis (PI. X., Fig. 2), the anterior 

 portion of the receptaculum is comparatively larger in 'niscctii.s 

 and its outline as a whole is somewhat different. 



I find that the coloring of this species is so variable that no 



