North American Fretsh-'icater (htracoda. 471 



The eye-spot, instead of being at the highest point of 

 the shell, as in the typical forms described by Vavra, is 

 slightly below and anterior to this location. The nata- 

 tory setae of the second antennae are long, reaching be- 

 yond the tips of the terminal claws by the length of 

 the claws, thus differing from C. villosa (Jurine), its 

 near relative, the natatory setae of which reach but to 

 the terminal claws. 



The caudal rami (Fig. 12) are rudimentary, the basal 

 part cylindrical, more than three times as long as wide, 

 then suddenly narrowing into a long flagellum, fully 

 twice as long as the basal part. The ramus also has a 

 dorsal seta at the termination of the basal part, slightly 

 longer than the ramus is wide. 



South Chicago, August 24, 1881, from a ditch open- 

 ing into the Calumet River (Coll. 111. State Lab. Nat. 

 Hist.). 



XIV. POTAMOCYPRIS BraDY. 



1868. Bairdia, Brady (6, p. 474). 

 1870. Potamocypris, Brady (7, p. 366). 



Second antennae four-segmented, third and fourth seg- 

 ments bearing numerous setae, which are short, not 

 reachiug beyond the middle of the terminal claws; last 

 segment with two strong terminal claws and two or 

 three short, slender setae. Mandible stout, palp three- 

 segmented and bearing a single branchial seta near the 

 base. Feet as in Cypris, caudal rami rudimentary, con- 

 sisting of a long seta with a lamellar base, bearing a 

 short dorsal one commonly at base of the lamellar part. 



Shell compressed, outline when seen from the side sim- 

 ilar to that of Cypridopsis. 



I know of but two species of this genus, — P. fidva 

 (Brady) and P. gregaria Sars, — neither of which is known 

 to occur in America. 



