428 Illinois State Laloratory of Natural History. 



■ Described from specimens found at the Biological Sta- 

 tion in a shore collection made at Thompson's Lake 

 (Station G), Havana, 111., May 26, 1895. 



Family CYPIIIDID.S]. 



"Shell generally thin and liorny; valves equal or hut 

 slightly unequal in size, surfaee usually smooth or sim- 

 ply punctated; ventral margins more or less sinuated ; 

 hinge margins edentulous. Eyes simple, usual].y conflu- 

 ent, sometimes wanting, Antennules (first antennae) 

 slender, usually seven-jointed, very flexile, usually pro- 

 vided with a number of long hairs forming a dense 

 brush. Antennae (second antennae) pediform, geniculated, 

 four- or five-jointed, clawed at the apex, second joint 

 mostly bearing an apical brush of haii's. 



"Mandibles strong, apex strongly toothed, palp four- 

 jointed, with a setiferous branchial plate at the base. 

 Two pairs of maxilla*, the first pair four-digitate, its 

 external branch distinctly two-jointed, bearing a large 

 setiferous branchial plate; second pair small, com- 

 posed of a single prehensile lobe and a palp which in the 

 female is generally simple, rarely pediform, and in the 

 male prehensile. Two pairs of feet dissimilar in struct- 

 ure, the anterior pair strong, ambulatory, directed down- 

 wards and having a long curved apical claw; posterior 

 pair bent backwards within the shell, and not used for 

 motion. Caudal rami usually well developed, elongated, 

 very mobile, and bearing two or three apical claws. In- 

 testine forming two dilatations, of which the anterior is 

 provided with ccecal appendages. Generative organs 

 large, and of complex structure, and partly extended 

 within the valves; in the male frequently a complex 

 whorled sac connected with the testis; copulatory or- 

 gans symmetrical, and of moderate size." — Brady and 

 Norman. 



I have thought it well to insert all the genera of good 

 workers in the following key, knowing that further 

 qisage will l>est determine their validity 



