Bo6 



FRESH-WATER BIOLOGY 



KEY TO NORTH AMERICAN FRESH-WATER OSTRACODA 



1 (2) Second antenna two-branched; one branch rudimentary, immobile, 



the other elongate, flexible, with long natatory setae (Myo- 

 docopa); or both branches well developed, movable, and 

 natatory (Cladocopa) ; or both branches flattened, similar 

 tofeet of the Copepoda(PLATYCOPA). . . Marine Tribes. 



These groups are not represented in fresh water so far as known. 



2 (i) Second antenna simple, subpediform, clawed at apex. Mostly fresh- 



water forms Tribe Podocopa . . 3 



3 (4) Three nearly similar pairs of legs. Furca rudimentary. Second ai(,- 



tenna with flageUum (Fig. 1251 (f^), and little adapted for 

 swimming Faniily Cytheridae . . 5 



4 (3) Two dissimilar pairs of legs. Furca commonly well developed. Sec- 



ond antenna without flageUum and commonly with natatory 

 setae 9 



5 (6) Parasitic on gills of Crustacea. Terminal claws of legs with four large 



teeth (Fig. 12490) Entocythere Ma.Tsha.ll igo}. 



Only one species of this genus known. 



Entocythere camharia Marshall 1903. 



Length 0.60 mm. Males abundant. Shell thin, frag- 

 ile and transparent. First antenna six-segmented. Sec- 

 ond antenna four-segmented. FlageUum unsegmented. 

 Caudal rami short and thick. Parasitic on gills of cray- 

 fish (Canibarus). Wisconsin. A most remarkable 

 form, in that Ostracoda rarely adopt parasitic habits. 



Fig. 1249. 



Entocythere cambaria. (a) End of third leg; 



(6) Side view, X 50. (After Marshall.) 



6 (s) Not parasitic. Crawlers or burrowers. Terminal claws of legs with 



not more than two teeth, or plain (Fig. 1260 (i). 



Limnicythere Brady 1868 . . 7 



7 (8) Shell decidedly reticulate, with two lateral furrows. Furca blunt. 



about three times as long as wide (Fig. 1250 a). 



Limnicythere reticulata Sharpe 1897. 



Length 0.66 to 0.70 mm. and o. 25 mm. wide. Grayish 

 white. Shell conspicuously marked with a honeycomb- 

 like network of polygonal reticulations, and deep lateral 

 furrows (Fig. i2Soi). Furca (Fig. 1250a) cylindrical, 

 thick and blunt, about three times as long as wide, with 

 two small setae. Posterior dorsal part of carapace tapers 

 to a point. Muddy bottom of ponds. Illinois, April. 



Fig. I2SO. 



Limnicylhm relicuhla. (a) Furca; (M Doiial view; 



(c) Side view, X J4. 



