THE WATER FLEAS (CLADOCERA) 



713 



iOS (104) Five to seven pre-anal spines; antennary setae ordinarily very long. 



Ilyocrypius spinifer Herrick 1884. 



Anus opens in depression on 

 dorsal margin of post-abdomen; 

 5-7 pre-anal spines; 4-8 post-anal 

 lateral spines in outer row. An- 

 tennary setae usually long, some- 

 times equaling length of valves; 

 in some specimens they are short, 

 apparently because of wear. Eight 

 to ten summer eggs; true ephip- 

 pium formed and cast off (Sars). 

 S unknown. Color yellow or red- 

 dish. Length, 9 . to 0.8 mm. 



This species is /. longiremis Sars; 

 /. halyi Brady. Not uncommon; 

 Maine to Lake Superior and Gulf 

 of Mexico- Probably in all regions 

 of United States. 



Fig. mo. Ilyocryptus spinifer. 



106 (103) Anus at end of post-abdomen; molting complete. 



Ilyocryptus acutifrons Sars 1862. 



0.1 MM. i 



Fig. nil. Ilyocryptus acutifrons. 



Post-abdomen not emarginate; about 8 

 small spines near claws, shortest next claw; 

 about 6 long, curved, lateral spines, about 8 

 marginal spines corresponding to pre-anals of 

 other species; the proximal two directed for- 

 ward; from distal spine of this set a series of 

 very small marginals to anus. Antennule club- 

 shaped, hairy. Ocellus nearer eye than inser- 

 tion of antennules. Claws as in /. sordidus. 

 Three to four summer eggs. $ unknown. 

 Color reddish or yellowish. Length, 9> ca. 

 0.7 mm. 



Rhode Island, Colorado 



107 (100, 116) Antennary setae • ~\ basal seta of 3-jointed ramus stout 



1-1-3 



and stiflE Macrothrix Baird 1843 . . 108 



Shape oval or rotund, somewhat compressed, with dorsal crest. Head large, ordinarily not 

 depressed; vertex evenly or abruptly rounded; rostrum short. Ventral margin of valves 

 ordinarily with long, stout, movable spines, which project in several directions. Antennules 

 large; lateral sense-hair near base. Antennae large; the proximal seta of 3-jointed ramus long, 

 stiff, and spinous; the others sparsely plumose or partly spinous. Five pairs of feet. No ab- 

 dominal process. Post-abdomen large; often bilobed. Claws small. Intestine simple, no ceca. 

 $ with large antennules; hook on first foot. 



108 (lis) Dorsal margin of head evenly rounded 109 



109 (114) Head extended; rostrum far from margin of valves. Antennules 

 enlarged near distal end. no 



