356 CRUSTACEA 



Key to the genera of Cytheridae here described : 



! Animals marine. 



&! Dorsal and ventral margins of shell not parallel 1. LOXOCONCHA 



5 2 Margins of shell nearly parallel. 



c t Surface of shell rough 2. CYTHEBEIS 



c 2 Surface of shell smooth 3. PSEUDOCYTHERETTA 



o 2 Fresh-water animals. 



6 X Animals free-swimming 4. LIMNICYTHEBE 



6 3 Animals parasitic 5. ENTOCYTHERE 



1. LOXOCONCHA Sars. Shell with a notch at the dorso-posterior 

 angle; ends and ventral margin extended into a flattened rim; first 

 antennae 6-jointed, with a group of slender setae on the last joint; sec- 

 ond antennae 4-jointed: 2 American species; marine. 



L. impressa (Baird) (Fig. 562). Length .82 mm.; height .51 mm.: 

 Vineyard Sound; very common in shallow water, among eel grass, 

 hydroids, etc. 



2. CYTHEREIS Sars. Shell strongly calcareous; first antennae 5 or 

 6-jointed; second antennae 4-jointed, with a short flagellum in the female; 

 first pair of feet differing on the two sides of the body in the male : 10 

 American species; marine. 



C. arenicola Cushman (Fig. 563). Shell quadrangular, the dorsal 

 and ventral margins being almost parallel, 1 mm. long ; .5 mm. high ; sur- 

 face with irregular patches, usually each with a single hair : common on 

 sandy bottoms in Vineyard Sound. 



Pig. 562 Fig. 563 Fig. 564 



Fig. 562 Loxoconcha impressa (Cushman). Fig. 563 Cythereis arenicola (Cush- 

 man). Fig. 564 Fseudocytheretta edwardsi (Cushman). 



3. PSEUDOCYTHERETTA Cushman. Inner border of shell irregular; 

 flagellum of second antennae 3-jointed; first foot of male with a seta on 

 the hinder border; left and right first feet of male very different: 1 

 species. 



P. edwardsi Cushman (Fig. 564). Dorsal and ventral margins of 

 shell nearly parallel, with rounded hairy ends; length 1.2 mm.; width 

 .61 mm. : Vineyard Sound in rather deep water, the commonest ostracod 

 of the region. 



4. LIMNICYTHERE Brady. First antennae 5-jointed with short bris- 

 tles on the outer edge; second antennae 4-jointed; mandible with large 

 branchial plate: 2 American species, both in Illinois. 



