616 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



20. Antennal area separated from head; trunk 4-segmented; caudal 



rami setiform; end segment of each leg with 1 apical seta; 



mouth of fishes cf Medesicaste Kr0yer, 1863 



Antennal area not separated; trunk 6-segmented; caudal rami 

 conical; end segment of each leg with 3 or 4 apical setae; 

 mouth of fishes c?" Strabax Nordmann, 1864 



21. Head and first 2 segments fused, bearing all the appendages 22 



Head and first segment only fused; second segment free and 



bearing second legs; each leg ramus cylindrical, with 2 apical 



setae; gills of fishes cf Ch.ondracanth.us La Roche, 1811 (p. 497) 



Head separated from thorax, first 2 free segments bearing legs 23 



22. First leg laminate, with 2 apical spines and an anterior process 



with 1 spine; second leg with a single spine; trunk 5-seg- 



mented; gills of fishes cT Oralien Bassett-Smith, 1899 (p. 494) 



Each ramus of both pairs of legs laminate, with 3 or 4 apical 

 setae; trunk made up of 4 segments; caudal rami setalike; 

 gills of fishes c? Acanthochondria Oakley, 1927 (p. 500) 



Each ramus laminate with 2 minute apical setae; trunk with 3 

 segments only; caudal rami conical, each tipped with 1 

 cilium; gills of fishes cT Chondracanthopsis, new genus (p. 508) 



23. Trunk 4-segmented; maxillipeds 3-segmented, with slender 



apical claw; caudal rami definitely longer than last trunk 



segment; gills of fishes cf Blias Kr0yer, 1863 (p. 493) 



Trunk 5-segmented; maxillipeds 2-segmented, with a stout 

 claw; caudal rami definitely shorter than last trunk seg- 

 ment; gills of fishes cf Trichthacerus Kr0yer, 1863 



24. First 2 pairs of legs biramose, rami 1-segmented; third and 



fourth pairs minute knobs; fifth pair biramose, rami 1- 



segmented; gills of fishes cf Diocus Kr0yer, 1863 



First 4 pairs of legs biramose, rami 2-segmented and well armed 

 with setae; fifth pair uniramose, 1-segmented, with 1 seta; 

 gills of fishes d^ Juanettia Wilson, 1921 



25. Macroscopic females, attached to the host 26 



Microscopic males, attached to the females 45 



26. Maxillipeds on inside of base of second maxillae, considerably 



behind the mouth; head narrowed, sometimes arched 



dorsally; gills of fishes ? Tracheliastes Nordmann, 1832 



Maxillipeds inside of second maxillae, both close to the mouth; 



head not narrowed, in line with trunk or bent forward 27 



Maxillipeds far behind the mouth; second maxillae equally 

 far behind maxillipeds; head not narrowed, in line with 

 trunk or bent backward 30 



Maxillipeds close to mouth; second maxillae far behind maxil- 

 lipeds; head narrowed, wormlike, in line with trunk or bent 

 backward 34 



27. Second maxillae much longer than the head; the latter separ- 



ated from the trunk by a groove, often by a short neck 28 



Second maxillae about the same length as the head; the latter 



completely fused with the trunk, the two unsegmented 32 



Second maxillae shorter than the head; the latter separated 



from the trunk; body faintly segmented; no caudal rami; 



gills of fishes 9 Vanbenedenia Malm, 1860 



