COPEPODS OF THE WOODS HOLE REGION 605 



3. Both first and fourth legs uniramose, second and third pairs 



biramose 4 



First legs only uniramose, second, third, and fourth pairs 



biramose 18 



Fourth legs only uniramose, first, second, and third pairs biramose 19 



First 4 pairs of legs biramose; fourth segment with dorsal plates 21 



4. Fourth, fifth, and genital segments fused, with a single dorsal 



plate, and a smooth conical process near each posterior corner; 



mouth of fishes 9 Dentigryps Wilson, 1913 



Fourth segment separated from fifth, with paired dorsal plates, 



overlapping the genital segment in female, rudimentary in male 5 



Fourth segment separated from fifth, without dorsal plates; gen- 

 ital segment with or without posterior processes 6 



5. Frontal plates with lunules; claws on first legs simple; genital 



segment with lobes and rudimentary legs at its posterior 



corners; outside of fishes cf 9 Tuxophorus Wilson, 1908 



Frontal plates without lunules; claws on first legs 3-pronged; 

 genital segment with horny toothed processes at its corners; 

 outside of fishes cf 9 Qloiopote3 Steenstrup and Liitken, 1861 (p. 415) 



6. Frontal plates with lunules; maxillae simple, spinelike 7 



Frontal plates without lunules; maxillae bifurcate or simple 14 



7. Genital segment simple, without processes or wings 8 



Genital segment with posterior processes as long as the abdomen 13 



Genital segment surrounded by a 2-lobed membranous wing; 

 abdomen also with a wing on either side, curling around the 

 ovisacs; gill cavity of fishes. 9 Parapetalus Steenstrup and Liitken, 1861 



8. Fourth segment produced into a long neck; genital segment 



many times larger than carapace; fourth legs 2-segmented; 



caudal rami fihform; gill cavity of fishes 9 Echetus Kr0yer, 1863 



Fourth segment short; genital segment usually much smaller, 



rarely a little larger than the carapace and depressed 9 



9. Furca and maxillary hooks both lacking 10 



Furca and maxillary hooks both present 11 



10. Genital segment shorter and narrower than the carapace; 



abdomen one-third the length of genital segment; caudal rami 

 wider than long; mantle of Nautilus.-- cf 9 Anchicaligus Stebbing, 1900 

 Genital segment longer than carapace; abdomen longer than 

 rest of body; caudal rami three times as long as wide, with 

 4 to 6 setae; gill cavity of fishes cf 9 Sciaenophilus Beneden, 1852 



11. Fourth legs rudimentary, 1-segmented; genital segment much 



wider than long; abdomen with only 1 segment; caudal rami 



large and stout; gill cavity of fishes cf 9 Pseudocaligus A. Scott, 1901 



Fourth legs normally developed, with 3 or 4 segments 12 



12. Males only; 3 terminal segments of fourth legs solidly fused 



and armed with spines coarsely flattened and broadly 

 winged; gill cavity of fishes, c?" Parapetalus Steenstrup and Liitken, 1861 

 Both sexes; 3 terminal segments of fourth legs loosely fused 

 and armed with setae or spines neither flattened nor winged; 



everywhere on fishes c? 9 Caligus Miiller, 1785 (p. 397) 



71937—32 40 



