North American Fresh-water Ostracoda. 421 



■Cypridojpds vidua O. F. Miiller. This cosmopolite seems 

 to occur quite uniformly in all kinds of waters 

 and at all seasons. 

 smaragdina Vdvra. Ditch entering Calumet R., Aug., 

 (2); found in July and August (Vavra). 



SYNOPSIS OF FAMILIES TREATED IN THIS PAPER.* 



1 (4). iSecond antennae simple, subpediform, geniculate, 



clawed at the apex, not very unlike the upper an- 

 tennae; both pairs of antennae bearing long setae 

 and adapted for swimming, or shortly setose and 

 not used for swimming. Mandibles distinct, mostly 

 strongly toothed at the lower extremity; palp of mod- 

 erate size, bearing a more or less developed branchial 

 appendage. First pair of maxillae bearing a large 

 branchial plate. Mosth^ fresh- water forms. 



Trihe Podocopa. 



2 (3). Three nearly similar pairs of feet, all directed 



downwards and used for locomotion. Caudal rami 

 obsolete, forming two rounded setiferous lobes. 

 Antennae very little adapted for swimming. 



Cytheride. 



3 (2). Two dissimilar pairs of feet; the anterior pair 



ambulatory, the posterior pair not used for locomo- 

 tion, bent backwards within the valves. Caudal rami 

 commonly well developed, mobile, and bearing two 

 terminal claws. Anteniue commonly with natatory 

 setae. Cypridid^. 



4 (1). Second antennae two-branched; one branch rudi- 



mentary, immobile, the other elongate, flexible, with 

 long natatory setae (Myodocopa); or both branches 

 well developed, movable, and natatorj'^ (Cladocopa); 

 or both branches flattened, similar to the feet of 

 the Copepoda (Platycopa). Marine tribes. 



* Modification of a key prepared by Brady (6). 



