3^6 CEUSTACEA 



with not more than 17 and second antennae with 4 segments: over 50 

 species, about 18 being American, all in fresh water, although some 

 species occur also in brackish and even in salt water; many species are 

 extremely variable in form. 



Key to the species of Cyclops here described : 



aj First antennae 17-jointed. 

 \ First antennae not reaching the hinder border of head segment, .C. VIRIDIS 

 6j First antennae reaching beyond this point. 



Ci Fifth feet with 2 long plumose terminal bristles C. leuckarti 



c. Fifth feet with 2 smooth terminal bristles C. BicusriDATUS 



C3 Fifth feet with 3 terminal bristles C. albidus 



ttj First antennae 12-jointed C. serrulatus 



ttj First antennae 10 or 11-jointed C. phalebatus 



C. leuckarti Claus (C. edax Forbes) (Fig. 543). Body slender and 



1.3 mm. long; first abdominal segment very long, equaling the other 3; 



first antennae 17-jointed; fifth feet 2-jointed, the second joint with 2 very 



long bristles, the outer one 



springing from the middle of 



the segment, the first joint also 



with a bristle: very common 



in the Great Lakes and in all 



, g * C parts of the country; Europe. 



r,. .r^o « 7 T T *. /o" T^ T^ ^v C. viildis Juriue (Fig. 



Fig. 543 — Cyclops leuckarti (Sussw. F. Deut.). 



A, furca and furcal bristles; B, fifth 544). Bodv 1.5 to 5 mm. long 



foot ; C, receptaculum seminis. . 



and variable in color, usually 



greenish; first antennae 17-jointed and very short, hardly reaching the 



hinder border of the head; fifth feet 2-jointed with a very broad basal 



joint, each joint bearing a plumose bristle. This species, which occurs also 



in Europe, is usually the commonest one in small ponds throughout the 



country. It is extremely variable, 



the 2 principal varieties being C. 



viridis var. hrevispinosus Herrick, 



which tends to the larger size, and J™** .-rr * iTMi 



C. viridis var. americanus Marsh ▼ « » o 



(C. insectus Forbes), the smaller ^ a * ' ^ 



and more numerous one. _, _^^ ^ . •.,• /o- ^ v^ r»«.,f \ 



Fig. 544 — Cyclops vindia (Sussw. F. Deut.), 

 C. biCUSpidatUS Claus (C. a, furca and f ureal bristles ; B, fifth 



^ foot ; C, receptaculum seminis. 



pulchellus Sars; C. forhesi Her- 

 rick) (Fig. 545). Body slender and 1.3 mm. long; first antennae 17- 

 jointed ; fifth feet 2-jointed, the terminal joint with 2 terminal bristles ; 

 furca and caudal bristles very long: veiy connnon over the entire country, 

 in lakes and rivers, being one of the commonest pelagic cyclops in the 

 Great Lakes; Europe. 



