FRESH-WATER BIOLOGY 



Spine of second segment of fifth foot stout, located at about middle 

 of segment; last three segments of female antenna with 

 delicate pectinate hyaline membrane. 



Cyclops strenuus Fischer 1851. 



It is one of the most common forms on the continent of Europe, but has 

 been found in America in only one locality, — a pond in the Adirondacks. It 

 is probable, of course, that it will be found in other localities, but it is a curi- 

 ous fact that hitherto it has been found only in a single collection. In its 

 general form it closely resembles viridis. 



Length of female, 1.35 mm. 



Fig. 1217. Fifth foot of Cyclops strenuus. X 358. (Original.) 



84 (81, 89) Second segment of fifth feet armed with two setae 85 



85 (86) Second segment of fifth feet elongate, inner setae spine-like, much 



shorter than outer. . . . Cyclops bicuspidatus Claus 1857. 



Fig. 1218. Abdo- 

 men of Cyclops bi- 

 cuspidatus. X 76. 

 (Original.) 



Fig. 1 2 19. Abdo- 

 men of Cyclops bi- 

 cuspidatus, var. 

 navus. X 62. 

 (Original.) 



Fig. 1220. Fifth foot 

 of Cyclops bicuspi- 

 datus. X 227. 

 (Original.) 



The furca of this species is very characteristic. It not only has a lateral seta at a little more 

 than one-half its length, but it has a httle depression armed with minute spines on its outer 

 margin at a little less than one-fourth of its length. These characteristics — the position of the 

 lateral seta, the lateral depression with the elongated furca — are presumptive evidence that a 

 species with seventeen segmented antennae is bicuspidatus. If, in addition, one can make out 

 the two terminal setae on the second segment of the fifth feet, he can be pretty certain of his 

 identification. Cyclops bicuspidatus is most commonly a limnetic species, and is the Cyclops 

 which may be considered as characteristic of the Great Lakes. While the form described and 

 figured is the common one, this species has varieties simila" to those noted for viridis, and we 

 sometimes find in pools a form agreeing in general structure with the typical forms, but with a 

 short furca. This modification was named navus by Herrick, and the name can be well retained 

 as a varietal distinction. Navus, however, is not so common in pools as the corresponding 

 variety of viridis. Fig. 12 18 shows the typical form of furca in bicuspidatus, and Fig. i2ig the 

 form in the variety navus. 



Length of female, i.i mm. 



86 (85) Second segment of fifth feet short, armed with two nearly equal 

 setae 87 



