576 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



126. Fifth legs made up of 3 segments 127 



Fifth legs made up of 2 segments, of the usual form 128 



Fifth legs made up of 2 segments but falciform; basal segment 



without inner expansion and outer process; body usually 



depressed; Httoral, among algae. __ cf 9 Alteutha Baird, 1845 (p. 192) 

 Fifth legs made up of 2 segments but completely fused; anal 



operculum finely ciUated; segments of first endopod equal; 



caudal rami as long as anal segment; fresh water, Serbia. 



9 Ceuthonectes Chappuis, 1924 



Fifth legs made up of a single segment, often rudimentary 174 



Fifth legs entirely lacking; rami of first 4 pairs of legs 3-seg- 



mented; second antennae 2-segmented, exopod obsolete; 



first antennae 8-segmented; littoral, muddy bottom. 



9 Aenippe Philippi, 1843 



127. First antenna 10-segmented; head with 6 long pectinated 



spines; both rami of the second antennae 4-segmented; 

 caudal setae longer than body; pelagic, 2,200 fathoms. 



9 Pontostratiotes Brady, 1883 

 First antennae 16-segmented; head without spines; endopod 

 of second antennae 4-segmented, exopod 6-segmented; 

 caudal setae half as long as body; littoral, muddy bottom. 



cf 9 Misophria Boeck, 1864 



128. Terminal segment of fifth legs 3-lobed, each lobe with a large 



plumose seta, basal expansion with 2 similar setae 129 



Terminal segment of fifth legs not 3-lobed, basal expansion 



usually with more than 2 setae 131 



129. Rostral plate ver}^ small; exopod of second antenna attached 



to basal segment of endopod; anal abdominal segment with 



2 stout dorsal claws; beach sands. cT 9 Arenosetella, new genus (p. 178) 



Rostral plate very large; exopod of second antenna attached 

 to side of second endopod segment; anal abdominal segment 

 without dorsal claws; littoral, muddy bottom. 



9 Ectinosomella G. O. Sars, 1911 



Rostral plate medium, but conspicuous; exopod of second 

 antenna attached to basal endopod segment; anal segment 

 without claws 130 



130. Terminal segment of fifth leg as wide as long; caudal rami 



usually shorter than anal segment; exopod of second 

 antenna always 3-segmented; muddy bottom, shallow. 



& 9 Ectinosoma Boeck, 1864 (p. 173) 

 Terminal segment of fifth leg much longer than wide; caudal 

 rami longer than anal segment; exopod of second antenna 

 often 2-segmented; muddy sand, shallow. 



cf 9 Pseudobradya G. O. Sars, 1904 



