COPEPODA FROM IFALUK ATOLL 11 



the females and males known at present, are based largely on such 

 characters. 



Key to the Species of Pseudocyclops 

 FEMALES 



1. Number of setae along internal margin of 3rd exopodal segment of leg 5 



reduced, the total armature of this segment being composed of 3 spines 

 at external margin, 1 spine at apex (at times pressed aside and inserting 



along internal margin), and 0-3 setae along internal margin 2 



4 setae along internal margin of 3rd exopodal segment of leg 5; in addition 

 there are 3 spines along external margin of that segment and 1 spine 

 at apex. (Compare P. crassiremis, in which the internal setae are very 

 small.) 5 



2. 3 fine, short setae along internal margin of 3rd exopodal segment of leg 5, in ad- 



dition to above-mentioned spines. Very small species (9 0.40-0.42 mm.), 



setae 2 and 3 of furca thickened at base. P. paulus Bowman and Gonzdlez 



0-1 seta along internal margin of 3rd exopodal segment of leg 5, in addition 



to above-mentioned spines 3 



3. No seta at internal margin of 3rd exopodal segment of leg 5; of 3 external 



marginal spines, the distal inserts almost apically, the apical spine inserts 

 internally. Endopodite of leg 5 2-segmented; segment 1 with strong 

 internal seta, segment 2 subpyriform, with several small, spiniform setae 

 and a transversal row of teeth ... P. cokeri Bowman and Gonzdlez 

 A single seta at internal margin of 3rd exopodal segment of leg 5, in addition 

 to the (displaced) apical spine and 3 external marginal spines 4 



4. Endopodite of leg 5 unsegmented, pyriform, with single strong, inter- 



nal seta and 3 transversal rows of teeth. Rostrum very strongly devel- 

 oped P. rostra tus Bowman and Gonzdlez 



Endopodite of leg 5, 3-segmented; segments 1 and 2 with strong spiniform 

 prolongation of external margin and internal seta, segment 3 with 1 

 external, 2 apical, and 1 internal seta, in addition to 2 rows of 

 teeth P. reductus Nicholls 



5. 1st segment of endopodite of leg 5 with seta at internal margin; endopodite 



of leg 5 either distinctly 3-segmented or 2nd and 3rd endopodal segments 



fused 6 



1st segment of endopodite of leg 5 without internal seta; endopodite of leg 

 5 composed of 1 or 2 free segments, but 1st and 2nd segments always more 

 or less fused 11 



6. 2nd and 3rd endopodal segments of leg 5 fused ; total number of setae on 5th 



endopodite 4: 1 (internal) on 1st, 1 (internal) on 2nd, and 2 (apical) on 3rd 



segment P. umbricatus Giesbrecht 



2nd and 3rd endopodal segments of leg 5 separate; total of setae on endop- 

 odite of leg 5 numbers 5-8 7 



7. 3rd endopodal segment of leg 5 with 6 setae: 2 at internal, 2 at external 



margin and 2 at apex 8 



3rd endopodal segment of leg 5 with 4 or fewer setae 9 



8. Cephalon and 1st thoracic somite separate, antennules 18-segmented. 



P. rubrocinctus Bowman and Gonzdlez 

 Cephalon and 1st thoracic somite fused, antennules 17-segmented. 



P. simplex Sewell 



