606 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



13. Four of these processes, 2 dorsal, 2 ventral; fourth segment 



small, of normal length; abdomen club-shaped and made up 

 of 2 segments; gills of fishes, ? Synestius Steenstrup and Liitken, 1861 

 Two dorsal processes only; fourth segment produced into a 

 long neck; abdomen same diameter throughout and 1-seg- 

 mented; mouth of fishes 9 Caligodes Heller, 1865 (p. 408) 



14. Genital segment without plates or processes; maxillae divided or 



simple; furca present 15 



Genital segment without plates, but often with processes; 



maxillae simple; furca lacking 17 



Genital segment covered with a fused dorsal plate, overlapping 



the abdomen; maxillae divided; furca well developed; outside 



of fishes d^$ Homoiotes Wilson, 1905 



15. Carapace deeply incised on frontal margin, 2 sides folded 



together on midline; fourth legs with 3 segments only; gills 



of fishes 9 Hermilius Heller, 1865 



Carapace depressed, but neither incised nor folded 16 



16. First maxillae divided; abdomen normally developed, with 



caudal rami attached to its posterior margin; fourth legs 

 4-segmented; outside of fishes. 



cT 9 Lepeophtheirus Nordmann, 1832 (p. 409) 

 First maxillae simple; abdomen wanting; caudal rami attached 

 to ventral surface of genital segment; fourth legs with only 

 3 segments; gills of fishes 9 Anuretes Heller, 1865 



17. Genital segment with 2 posterior processes longer than the 



segment itself; abdomen five times as long as wide and con- 

 cealed; gills of fishes 9 Diphyllogaster Brian, 1899 



Genital segment without processes; maxillae znere rudiments; 

 abdomen only twice as long as wide, 2-segmented, wholly 

 visible; mouth of fishes cf 9 Abasia Wilson, 1908 



18. Both rami of fourth legs 3-segmented; abdomen longer than 



genital segment; fourth segment without dorsal plates; max- 

 illae bifurcate; outside of fishes 9 Calistes Dana, 1849 



Fourth exopod 3-segmented, endopod 2-segmented; abdomen 

 shorter than genital segment; fourth segment with dorsal 

 plates; maxillae simple; gills of fishes..' 9 Caligeria Dana, 1849 



19. Frontal plates with lunules; maxillary hooks and furca both 



present; basal abdomen segment lobed in female, not lobed 



in male; outside of fishes c?" 9 Midias Wilson, 1911 



No lunules, maxillary hooks, or furca; basal abdomen segment 

 lobed in female, not lobed in male; exopods with horny 

 processes; outside of sharks. - cT 9 Alebion Kr0yer, 1863 (p. 418) 



Frontal plates without lunules; abdomen without lobes 20 



20. No maxillary hooks or furca; fourth segment without dorsal 



plates; genital segment with 2 ventral horny processes; max- 

 illae divided; outside of fishes c? 9 Calina Beneden, 1892 



Maxillary hooks and furca present; fourth segment with rudi- 

 ments of dorsal plates; genital segment without processes; 

 maxillae simple; mouth of fishes c? 9 Paralebion Wilson, 1911 



21. Both rami of fourth legs 2-segmented; furca present; genital 



and basal abdominal segments without lobes or leg rudiments; 



in surface tow cf 9 Dysgamus Steenstrup and Liitken, 1861 



Fourth exopods 3-segmented, endopods 2-segmented; genital 

 and basal abdominal segments with lobes in female, without 

 them in male 22 



