COPEPODS OF THE WOODS HOLE REGION 433 



rate; fourth and genital segments with fused plates, covering the 

 full width of the body ; sixth segment represented by a median lobe 

 attached to the posterior sinus of the genital segment. Abdomen 

 2-segmented, hidden dorsally by the sixth segment lobe and ven- 

 trally by a short and wide plate ; caudal rami in the form of dentate 

 processes attached to the sides of the ventral plate at its base. Four 

 pairs of biramose swimming legs, all the rami laminate and 2-seg- 

 mented, but the segments more or less fused; no fifth or sixth leg 

 rudiments. 



Male. — The original type of the genus NogauS; head fused with 

 first segment; carapace broad, with convex sides, posterior lobes 

 curved inward, the margin between them with a pair of secondary 

 lobes; eyes usually visible. Second segment with lateral dorsal 

 plates, third and fourth segments without them; genital segment 

 moderately enlarged, with rudiments of fifth and sixth legs; no 

 separate sixth segment. Abdomen 2-segmented, segments subequal; 

 caudal rami foliaceous, each with three or four large plumose setae. 

 Rami of first four pairs of legs distinctly 2-segmented. 



KEY TO THE SPECIES 



FEMALES 



1. Dorsal plates of fourth segment reaching well beyond center 



of genital segment; sixth segment plate longer than wide 2 



Dorsal plates of fourth segment not reaching center of genital 



segment; sixth segment plate as wide as long or wider 3 



2. A distinct median plate on second segTaent, between bases of 



lateral plates; third segment plates not fused smithii (p. 434) 



No median plate on second segment ; third segment plates fused 



across midline, with a shallow median sinus cranchii (p. 435) 



3. Second segment plates not reaching beyond tips of third segment 



plates; median sinus of latter short and narrow bicolor (p. 436) 



Second segment plates reaching half their length beyond tips of 



third segment plates; sinus of latter wide and deep sinuatus (p. 437) 



MALES 



1. Carapace, including lobes, longer than wide ; second, third, and 



fourth segments as wide as genital segment ; abdomen wider 



than long smithii (p. 434) 



Carapace wider than long; fourth segment considerably nar- 

 rower than genital segment ; abdomen as long as wide 2 



2. Length of carapace on midline one-third of body length ; sixth leg 



rudiments larger than fifth, triangular, acuminate cranchii (p. 435) 



Length of carapace on midline nearly one-half of body length ; 



sixth leg smaller than the fifth 3 



3. Caudal rami one-half longer than wide, each with 4 apical setae, 



equidistant from one another bicolor (p. 436) 



Caudal rami scarcely longer than wide, inner seta not apical and 



far removed from other three sinuatus (p. 437) 



