COPEPODS OF THE WOODS HOLE EEGION 159 



hooks on the head, and by the fifth legs. This is a tropical form that 

 only occasionally wanders this far north in the Gulf Stream. 



Family ACARTIIDAE 



Genus ACARTIA Dana, 1846 



Metasome spindle-shaped, strongly narrowed at both ends ; urosome 

 one-third as long as metasome ; genital segment as long as the two 

 abdominal segments combined ; exopods of first four pairs of legs 

 3-segmented, endopods 2-segmentecl; fifth legs uniramose in both 

 sexes, symmetrical in the female, the last segment spiniform or seti- 

 form, asymmetrical in the male, the right leg the larger. 



KET TO THE SPECIES 



1. Posterior corners of fifth segment produced into short, stout 



spines ; end segment of fifth leg half as long as plumose seta 



on preceding segment; its distal third densely toothed danae (p. 160) 



Posterior corners of fifth segment smoothly rounded, spines 

 lacking or on the dorsal surface of the segment 2 



2. Front of head carrying 2 tentacular filaments below 8 



Front of head without any trace of tentacular filaments below 4 



3. Caudal rami scarcely longer than wide ; end segment of fifth 



legs stout and as long as plumose seta on preceding segment, 



toothed at center, then abruptly narrowed tonsa (p. 160) 



Caudal rami twice as long as wide; end segment of fifth legs 

 stout, evenly tapered, ciliated, and as long as plumose seta on 

 preceding segment bifilosa (p. 162) 



4. Caudal rami dilated into spheres, nearly as wide as long; their 



setae conspicuously dilated at their bases discaudata (p. 163) 



Caudal rami normal laminae, setae not dilated 5 



5. End segment of fifth legs stout, straight, and as long as plumose 



seta on precedmg segment clausii (p. 164) 



End segment of fifth legs slender, bent at the center, and much 



longer than plumose seta on preceding segment longiremis (p. 165) 



1. Front of head carrying 2 tentacular filaments below 2 



Front of head without any trace of tentacular filaments below 3 



2. Second segment of right fifth leg notched and armed with a short 



spine, end segment of left leg with angular process, both on 



inner margin bifilosa (p. 162) 



Second segment of right fifth leg and end segment of left leg 

 with smooth inner margins tonsa (p. 160) 



3. Right fifth leg more than twice as long as left, the first 2 free 



segments at the base very unequal in length discaudata (p. 163) 



Right fifth leg but little longer than the left; the first 2 free 



segments at the base subequal in length 4 



4. End segment of right fifth leg stout, considerably swollen in the 



middle, its outer margin perfectly smooth longiremis (p. 165) 



End segment of right fifth leg slender, but little swollen in middle, 



its outer margin armed with 3 to 5 spines clausii (p. 164) 



