THE WATER FLEAS (CLADOCERA) 689 



KEY TO NORTH AMERICAN FRESH-WATER CLADOCERA 



i (248) Body and feet covered by a bivalve shell. Feet in general foliaceous, 

 not plainly jointed. . . . Section A. Calyptomera . . 2 



i (21) Six pairs of feet, all similar, except the last, and all foliaceous. 



Tribe I. Ctenopoda . . 3 



3 (18) Shell of ordinary type. Antenna biramous in female, rami flattened, 



the dorsal with numerous setae, both lateral and terminal. 



Family SIDIDAE Baird . . 4 



Head large; cervical sinus present. Antennules large, movable. Antennae with terminal 

 setae only on ventral ramus. Eye large, with numerous lenses; ocellus small or absent. Intes- 

 tine simple, usually with more or less distinct median cecum or enlargement at anterior end; 

 rarely with 2 hepatic ceca. Heart elongated. Male usually with characteristic antennule; 

 the flagellum united with the base into one structure, long, tapering, with a row of fine spinules 

 toward apex; usually with grasping organ on first foot and copulatory organs on post-abdomen. 



4 (5) Dorsal ramus of antenna 3-jointed, rostrum present. 



Sida Straus 1820. 



Head with large gland on dorsal side; pointed rostrum; no fornices. Antennules of 9 

 attached to side of rostrum, short, truncate, with short flagellum. Ventral ramus of antennae 

 2- jointed. Antennules of $ very long; no copulatory organ; first foot with hook. 



Only one American species. . . Sida crystalline, (O. F. Muller) 1785. 



FIG. 1051. Sida crystallina. (Unless otherwise indicated all figures were drawn especially for this 



chapter.) 



Color yellowish-hyaline, sometimes with brilliant blue spots. Length, 9, 3-0-4-0 mm.; 

 $ , 1.5-2.0 mm. 

 Common in lakes and ponds among weeds. 



5 (4) Dorsal ramus of antenna 2-jointed 6 



6 (9) With lateral expansion on basal joint of dorsal ramus of antenna. 



Latona Straus 1820 . . 7 



Large, tongue-shaped projection on ventral side of head, its ventral surface concave. Ventral 

 ramus of antennae 3-jointed. Long setae on posterior margin of valves. Eye dorsal, far from 

 optic ganglion. $ with copulatory organ; no hook on first foot. 



