566 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



43. Fifth leg quadrangular, tipped with 8 unequal setae in fenaale, 



6 in male; second exopod in male with huge apical falciform 



claw; muddy sand, 20 fathoms c? 9 Cylindropsyllus Brady, 1880 



Fifth leg with 3 unequal apical setae; a fourth seta attached to 

 outer process near the base; distal half of caudal rami abruptly 

 narrowed (Norwegian coast). 9 D'ArcythorapsoniaT. Scott, 1906 (p 291) 



44. Endopod of first leg definitely longer than exopod; fifth leg 



triangular, with a stout apical spine, 3 inner setae and 1 



outer; sandy bottom, 30 fathoms. _ ? Leptastacus T. Scott, 1906 (p. 252) 



Exopod of first leg longer than endopod; fifth leg with 2 large 

 outer spines and 6 setae in female, with 6 setae only in the 

 male; littoral, 20fathoms c? 9 Stenocaris G. O. Sars, 1909 (p. 286) 



Exopod of first leg longer than endopod; fifth leg with 2 apical 

 setae in female, 4 in male; second and third endopods modi- 

 fied in male; brackish water, among algae cf 9 Horsiella Gurney, 1920 



45. Basipods of swimming legs geniculate, projecting laterally; 



body segments separated by conspicuous constrictions, often 



angular; littoral, among algae cf Laophontodes T. Scott, 1894 



Basipods of swimming legs neither geniculate nor projecting; 



body segments not separated by conspicuous constrictions 46 



46. Exopod of second antenna replaced by a seta; both third and 



fourth endopods modified for prehension in male, and both 

 2-segmented; fresh water (Germany), cf 9 Wolterstorffia Schmeil, 1894 

 Exopod of second antenna 1-segmented and tipped with setae; 



fourth endopods not modified in male 47 



47. Setae of second legs elongated, naked, branched at tips; setae 



of fifth legs greatly enlarged basally in female, but not in 



male; beach sands cf 9 Quintanus, new genus (p. 258) 



Setae of second and fifth legs normal, neither branched at tips 



nor enlarged at base; third endopod modified in male 48 



48. Endopod of second legs reaching distal end of second segment 



of exopod, with 1 long apical plumose seta, 2 inner, 1 outer 

 naked setae (lakes in Peruvian Andes), cf 9 Godetella Delachaux, 1918 

 Endopod of second legs scarcely reaching proximal end of 

 second segment of exopod, with 2 short, equal apical and 1 

 outer setae, all 3 plumose; fresh or brackish water. 



cf 9 Cletocamptus Schmankevitsch, 1875 



49. Basipods of swimming legs geniculate, projecting beyond the 



lateral margins of the body; fifth legs long and narrow 50 



Basipods of swimming legs not geniculate nor projecting lat- 

 erally; fifth legs variously shaped 52 



50. Rami of first legs subequal; body with a row of uniform, sharply 



pointed lappets on each side, 1 on each segment except last 



2; muddy bottom, shallow cf 9 Arthropsyllus G. 0. Sars, 1909 



First endopod much longer than exopod; body without lappets; 



segments of second and third endopods often indistinct.. 51 



51. Body segments with rounded lateral lobes, but no spines; first 



endopod with stout, curved, spinelike claw and 1 seta at the 



tip; Uttoral, shallow 9 Laophontodes T. Scott, 1894 



Body segments, except last 2, with curved, often branched, 

 denticulate spines in 6 rows, lateral and dorsal; first endopod 

 with 3 apical setae; muddy bottom 9 Ancorabolus Norman, 1903 



Neither lateral lobes nor spines; first endopod with 4 apical 

 setae; end segment of fifth leg 10 times as long as wide, nar- 

 rowed distally; muddy bottom cf 9 Malacopsyllus G. O. Sars, 1911 



