278 



UNIVERSITY OF COLORADO STIIDIES 



38 (69) Ventral branch of antenna 3-jointed; dorsal branch 4-jomted (first 

 joint may be very short). Intestine usually without convolution 39 



39 (60) A pair of blind diverticula at anterior end of gut (Fig. 26). Anten- 

 nules usually small and inconspicuous. 5 pairs of feet. 



Family Daphnidae 40 



40 (53) Head beaked below; never sharply separated from body above. 

 Eye of only moderate size 41 



41 (48) Shell with sharp spine at upper posterior angle. Genus Daphnia 42 



42 (45) Claw of post-abdomen with pecten. Anal spines not increasing very 

 greatly in length toward end of series 43 



43 (44) Front of head about evenly curved to end of beak; head of young 

 crested. Fornix with spine just back of base of antenna and extended well 

 back on side of carapace. Distal pecten of about 15 spines not sharply 

 distinct from the finer spines extending to end of claw. Post-abdomen with 

 many clusters of fine spines on sides. Length up to 2.8 mm. 



Daphnia psittacea Baird 



La Junta, in cattle ponds. [Nebraska, Colo- 

 rado. From Greenland to Algiers and Palestine.] 



Fig. 22. — Daphnia psittacea. Post-abdomen. 



Fig. 23. — Daph; 

 b, young female. 



psittacea. fl, mature female; 



(43) 



Front of head concave between eye and beak. Fornix without spine 

 Distal pecten of 4-1 1 very distinct spines. Very, 

 variable in form and size. Local varieties very 

 different from figures may commonly be expected. 

 Many forms now considered as varieties have 

 been described as distinct species. Immature 

 specimens of some varieties have an angle or a 

 crest bearing teeth on the carapace above the 

 heart. Length up to 2 . 5 mm. 



Daphnia pulex De Geer 



In all parts of state from plains to highest mountain lakes. 

 [World-wide.] 



■Daphnia pulex. 



