NO. 1573. PA RASITIC COPEPODS— WILSON. 437 



NESIPPUS BOREALIS Steenstrup and Lutken. 

 Plate XXXVII. 



Nogagus borealis Steenstrup and Lutken, ISfil, p. 387, pi. xi, fig. 21. — Bas- 

 sett-Smith, 1899, p. 4()0. 



Male. — Carapace strongly arched dorsally, about the same length 

 and width, exclusive of the posterior lobes; narrowed anteriorly to a 

 broad and rounded knob which projects over and some distance in 

 front of the proximal ends of the frontal plates. Eyes large, placed 

 far forward on either side of the median line, in contact with each 

 other, but not fused. The frontal plates are enlarged at their distal 

 ends and evenly rounded, and they cover the l)asal joints of the first 

 antenna?. Posterior lobes narrow and reaching a little beyond the 

 center of the second thorax segment; posterior margin between the 

 lobes slightly concave and perfectly smooth. The projection of the 

 carapace forward and the comparative shortness of these lobes is 

 probaldy due to shrinkage in the alcohol, and is not the normal con- 

 dition. The entire body of the copepod is perceptibly curled over 

 ventrally, bringing the large conspicilla in front of the eyes on the 

 very margin in a dorsal view. 



Free thorax segments, chiefly noticeable for their great length and 

 contracted width, the two combining to produce an excepti(nially 

 elongated appearance. Some of tliis is no doubt due to the same 

 shrinkage just mentioned, for the segments are all strongly arched 

 and the lateral processes on the first one are turned over toward the 

 ventral surface so as to be nearly invisible tlorsally. But the shrink- 

 age can have practically nothing to do with the length of the segments, 

 so that the species is an elongate one under any conditions. In the 

 figure given l)y Steenstrup and Lutken there has evidently not l)een 

 as much shrinkage as in the present specimen. 



The first free segment is seen to be considerably wider than the 

 two following ones, with nearly straight sides and very small, tri- 

 angular lateral lobes. The free segments together are the same length 

 as the carapace on the mid-line, and the fourth one is three-fifths the 

 width of the second and the same width as the genital segment. 



The latter is longer than wide, with rather sharp corners and slightly 

 convex sides. There are no traces of rudimentary legs either on the 

 lateral margins or the posterior corners. 



Posteriorly where it joins the abdomen the segment is narrowed 

 into a sort of neck, and is traversed, on both the dorsal and ventral 

 surfaces, by a pair of longitudinal furrows, one on either side, a short 

 distance from the lateral margin. The ventral surface is flat through- 

 out, while the dorsal surface between the furrows is strongly arched. 



Abdomen one-jointed and triangular, with well-rounded angles, one 

 of which, slightly incised, points backward between the anal laminge. 



