346 



CRUSTACEA 



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 : 



! First antennae 17-jointed. 



&! First antennae not reaching the hinder border of head segment.. C. VIBIDIS 

 & 2 First antennae reaching beyond this point. 



d Fifth feet with 2 long plumose terminal bristles C. LEUCKABTI 



c a Fifth feet with 2 smooth terminal bristles C. BICUSPIDATUS 



c 3 Fifth feet with 3 terminal bristles C. ALBIDUS 



2 First antennae 12-jointed C. SERBULATUS 



03 First antennae 10 or 11-jointed C. PHALEBATUS 



C. leuckarti Glaus (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 

 parts of the country; Europe. 

 C. viridis Jurine (Fig. 

 544). Body 1.5 to 5 mm. long 

 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. brevispinosus Herrick, 

 which tends to the larger size, and 

 C. viridis var. americanus Marsh 

 (C. insectus Forbes), the smaller 

 and more numerous one. 



C. bicuspidatus Glaus (C. 

 pulchellus Sars; C. forbesi 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; 

 f urea and caudal bristles very long : very common over the entire country, 

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

 Great Lakes; Europe. 



Fig. 543 Cyclops leuckarti (Sflssw. F. Deut.). 



A, furca and furcal bristles ; B, fifth 



foot ; C, receptaculum seminis. 



B 



Fig. 544 Cyclops viridis (Siissw. F. Deut.). 



A, furca and furcal bristles ; B, fifth 



foot ; C, receptaculum seminis. 



