HIGHER CRUSTACEANS (MALACOSTRACA) 



845 



30 (31) Chelae of peraeopods weak, subequal, fingers with terminal hair- 

 tufts . Family ATYIDAE. 



Only species in North America. . . Palaemonias ganteri Hay 1903. 



A typical and char- 

 > acteristic fresh-water 

 group, abundant in the 

 tropics, but certain 

 forms are found in tem- 

 pera te regions, and 

 their distribution is 

 quite peculiar, they 

 being found at rather 

 isolated localities, re- 

 mote from each other. 

 This discontinuity is a 

 mark of antiquity of 

 the group. One of 

 these isolated forms is 

 found in North Amer- 

 ica, Palaemonias ganteri 



Hay, and is blind, living in Mammoth Cave in Kentucky. The nearest place where related 



forms are found is in the West Indies. 



FIG. 1311. Palaemonias ganteri flay. 



(After Hay.) 



31 (30) Chelae of peraeopods inequal, the second pair larger, often much 

 larger, than the first, and very strong. Fingers without 

 terminal hair-tufts. . . . Family PALAEMONTDAE . . 32 



A family abundant in the sea, but also of great importance in the fresh water. All transi- 

 tional stages between life in the sea and in fresh water are found here. 



32 (33) Mandible without palpus. Second pair of peraeopods only slightly 

 larger than the first, both of them rather weak. Size of 

 body medium. . . . . . ; :, . . . Palaemonetes Heller. 



Contains a number of species 

 which live in salt and brackish 

 water. One of them (P. vulgaris 

 Say) is found along our Atlan- 

 tic coast. Other species have 

 become true fresh- water forms: 

 Two have been described from 

 the United States: P. paludosa 

 Gibbes and P. exilipes Stimp- 

 son, both from Carolina, but they 

 are supposed to be identical. 

 This form has also been found in Florida, in the Illinois River, and in Lake Erie. 



FIG. 1312. Palaemonetes exilipes Stimpson. X i. (After Smith.) 



33 (32) Mandible with palpus. Second pair of peraeopods, in the male, 

 excessively developed, very long (often longer than the 

 whole body), with strong chelae. Size of body considerable. 



Palaemon Fabricius. 



This genus (sometimes, but erroneously, called Bithynis) is extremely abundant in the fresh 

 water of the tropics. Only one species is recorded from the United States: P, ohionis Smith, 

 which is found in the Mississippi and lower Ohio Rivers (up to Cannelton, Ind.). Little 

 more is known about this species than that it exists and that it is locally used as food. (Not 

 even a figure of it has been published.) 



