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sexes, the endopod two-jointed and longer than the exopod 

 in the female, wanting in the male. The copulatory organs 

 possess the three processes on the inner lobe, but the spine- 

 shaped process is nearly straight and nearly parallel with 

 the two others which are inserted on the end of the lobe ; 

 the lateral process is never hook-shaped and an additional 

 process wanting. 



The 6 species of the genus may be divided into two 

 groups separated by some sharp characters. 



A. Maxillulae with a pseudexopod well developed. First 

 elongate pair of legs with long spines both from the 

 terminal joint and from the distal angle of the penul- 

 timate joint. Second to fifth pair of legs with the full 

 number of joints, therefore three joints beyond the 

 knee. 



B. Maxillulae without pseudexopod. First pair of legs 

 with long spines only from the terminal joint. Second 

 and third pairs of legs with but two joints beyond the 

 knee, fourth and fifth pairs with one joint beyond the 

 knee. 



Group A. 



This group comprises N. megalops G. O. S. and 

 N. difficilis n. sp. N. megalops is known only from the 

 Atlantic. 



N. difficilis n. sp. — At least by a preliminary exami- 

 nation I have not found any other reliable character 

 between this Pacific form and the Atlantic N. megalops 

 than differences in the terminal and proximal processes of 

 the male copulatory organs. But as the two processes 

 afford excellent characters in the other species of the 

 genus, I was forced to establish N. difficilis as a new 

 species. And three adult males are to hand of N. difficilis, 

 and a good number from various parts of the North 

 Atlantic of N. megalops. 



In both species the terminal process has its proximal 

 part directed somewhat outwards, and then the process 



