COPEPODS OF THE WOODS HOLE EEGIOK 215 



Genus AMPHIASCUS G. O. Sars, 1905 



Body slender and cylindrical ; head fused with the first segment ; 

 urosome 4-segniented in female, 5-segmented in male, not sharply 

 defined from metasome; rostrum often large and prominent; genital 

 segment imperfectly divided in female, entire in male. First 

 antennae 8-segmcnted; exopod of second antennae 3-segmented, the 

 middle segment very short; rami of first four pairs of legs 3-seg- 

 mented; second endopod modified in male; fifth legs 2-segmented, 

 large and foliaceous in female, much smaller in male. Two ovisacs. 

 Body showing distinctive coloration in the different species. 



KETi' TO THE SPECIES 



1. Terminal segment of fifth legs with 7 marginal setae, the third 



inner one nonplumose and hairlike ; entire body, except dorsal 



surface of head, dark chocolate-brown obsciirus (p. 216) 



Terminal segment of fifth legs with 6 marginal setae, the second 

 and third inner ones nonplumose and hairlike; body light 

 colored 2 



Terminal segment of fifth legs with 5 marginal setae, the middle 



one nonplumose and hairlike; l)ody light colored 8 



2. Longest apical seta of caudal rami with a conspicuous swelling 



at its base, overlapping t!ie seta outside of it 3 



None of the apical setae of caudal rami swollen at their base 4 



3. Exopod of first legs as long as basal endopod segment or longer ; 



rostrum slender and acuminate longirostris (p. 217) 



Exopod of first legs distinctly shorter than basal endopod seg- 

 ment ; rostrum broadly triangular and blunt attenuatus (p. 218) 



4. Exopod of first legs definitely longer than basal endopod segment ; 



eye not visible pallidas (p. 219) 



Exopod of first legs definitely shorter than basal endopod seg- 

 ment ; eye visible 5 



5. Two distal segments of first endopod about same length and 



together much less than half the length of basal segment 6 



End segment of first endopod twice as long as second segment, 

 the two together much more than half the length of the basal 

 segment 7 



6. End segment of third exopod with 2 apical setae and 1 on inner 



margin; adults less than 0.5mm. long parvus (p. 221) 



End segment of third exopod with 2 apical setae and 3 on inner 



margin; adults more than 0.75 mm. long cinctus (p. 221) 



7. End segment of third exopod with 2 apical setae and 1 on inner 



margin; caudal rami twice as wide as long sinuatus (p. 222) 



End segment of third exopod with 2 apical setae and 3 on iniier 



margin ; caudal rami twice as wide as long- dactylifer, new species (p. 223) 



8. Caudal rami longer than wide ; outer apical seta swollen at its 



base hispidus (p. 225) 



Caudal rami twice as wide as long ; outer apical seta not swollen 

 at its base 9 



