582 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



172. Basal expansion of fifth legs not reaching midUne, with 2 setae; 



end segment with 3 marginal, 1 dorsal setae, the 2 segments 



often fused; sandy bottoms cf Bradya Boeck, 1872 



Basal expansion of fifth legs on the midline, with 1 seta only, 

 far removed from the end segment, which is armed with 4 

 marginal setae; muddy bottoms, cf 9 Pseudotachidius T. Scott, 1898 



173. Each basal expansion of fifth legs with 6 setae and an inner 



fringe of interlaced spines; end segment spatulate, also with 



6 stout setae; beach sands cf 9 Rathbunula, new genus (p. 297) 



Each basal expansion of fifth legs with 5 setae, without the 

 fringe of spines; end segment broad and laminate, with 4 or 5 

 smallish setae; littoral, among algae... 9 Thompsonula T. Scott, 1905 



174. Exopod of second antenna 1-segmented, often rudimentary 175 



Exopod of second antenna 2-segmented 176 



Exopod of second antenna 3-segmented 178 



Exopod of second antenna 6- or 7-segmented 180 



175. Endopod of second antenna 3-segmented, exopod rudimen- 



tary, with a single minute seta; thoracic segments without 



spines; fifth leg normal; pelagic 9 Hensenella Dahl, 1895 



Endopod of second antenna 2-segmented; first 4 thoracic 



segments each with a stout dorsal spine; fifth leg leaf -like, 



with 4 simple setae; pelagic (Antarctic Ocean). 



9 Tetanopsis Brady, 1910 

 Endopod of second antenna 4-segmented; thoracic segments 



without spines; fifth leg linear, with 2 apical and 3 outer 



lanceolate, dentate setae; pelagic, surface tow. 



(f" 9 Aegisthus Giesbrecht, 1891 (p. 304) 



176. Basal segment of first endopod the same length and width as 



second segment; end segment with 4 setae; fifth leg angular, 

 in female 8, in male 6 setae; brackish water. 



d' 9 Tachidius Lilljeborg, 1853 (p. 294) 

 Basal segment of first endopod much longer than second segment 177 



177. Fifth leg divided by a median sinus into 2 rounded lobes, each 



with 5 setae; first endopod with 2 stout apical claws and 1 



seta; littoral, shallow _. 9 Idomenella T. Scott, 1906 



Fifth leg tapered to a single blunt apex, with 4 setae and 2 

 spines; first endopod with 3 weak apical setae, without the 

 claws; washed from dredgings cT 9 Alteuthella A. Scott, 1909 



178. Endopod of second legs 2-segmented, much modified; segments 



of fifth legs fused; each with 3 or 4 setae; rudiments of sixth 

 legs behind the fifth pair; muddy bottoms. 



cf Stenhelia Boeck, 1864 (p. 228) 

 Endopod of second legs 3-segmented and unmodified 179 



179. Segments of first endopod the same length, end segment with 



5 setae; each fifth leg 2-lobed, outer lobe with 4, inner with 



2 setae; littoral, 30 fathoms 9 Bradya Boeck, 1872 



End segment of first endopod much the longest, with 2 pecti- 

 nated spines and 2 inner setae; each fifth leg 1-lobed, with 



4 setae; beach sands 9 Echinocornus, new genus (p. 301) 



End segment of first endopod the longest, with 3 apical and 1 



inner seta; each fifth leg a minute 1-segmented lamina with 



5 unequal setae; littoral, 2 fathoms 9 Brianola Monard, 1926 



