HIGHER CRUSTACEANS (MALACOSTRACA) 843 



17 (18) Outer ramus of third uropods uniarticulate. 



Eucrangonyx Stebbing. 



Five species are known, living in ponds, springs, and wells. Eyes either well developed or 

 more or less rudimentary. One species is blind. 



18(17) Outer ramus of third uropods biarticulate NiphargusTfay. 



A single species in caves in Tennessee, with the eyes wanting or very rudimentary. 



19 (16) Inner ramus of uropods not rudimentary, one-half or three-fourths 



as long as the outer. Telson cleft to the base or nearly so. 



Gammams Fabricius. 



Six species, two of them (G. fascialus Say 

 and G. limnaeus 'Smith), rather abundant in 

 rivers, lakes, and smaller bodies of water. 

 The other species are more local. Eyes 

 present, but one species is a blind cave- 

 form of Cuba. 



FIG. 1308. Gammarus limnaeus Smith. X 2. 

 (After Smith.) 



20 (15) Telson entire 21 



21 (24) Third uropods with rami 22 



22 (23) Third uropods uniramus. Telson short and broad. Crangonyx Bate. 



Three species are known, all without eyes, living in caves and wells, and with very local 

 distribution (Kentucky, Indiana, Connecticut, Wisconsin). 



23 (22) Third uropods biramous, inner ramus rudimentary, outer uniarticu- 



late. Telson long Stygonectes Hay. 



Only one blind species, found in an artesian well in Texas. 



24(21) Third uropods without rami. ..,.,. A pocrangonyx Stebbing. 

 One species, blind, from a well in Illinois. 



25(12) Antennulae without secondary flagellum. Telson entire. Third uro- 

 pods uniramous . . Family ORCHESTTIDAE. 



This family is abundantly represented in the sea. 



Only one genus and species in the fresh water of North America. 



Hyalella knickerbockeri (Bate) 1862. 



This species possesses a very wide 

 range, and is found in rivers, ponds and 

 lakes from Maine to Florida and Cali- 

 fornia (and extends southward into Cen- 

 tral America). This genus (Hyalella) is 

 remarkable for the fact that all its spe- 

 cies are found exclusively in fresh water 

 and are restricted to North and South 

 America. 



FIG. 1309. Hyalella knickerbockeri Bate. 

 X5- (After Smith.) 



26 (i) With a carapace. Eyes upon movable eye-stalks. Thoracic limbs 

 with or without exopodites, one, two, or three of the ante- 

 rior pairs modified as maxillipeds 27 



