NO. 1573. PA RASITIC COPEPODS— ^ VILSON. 418 



ages and the legs are very similar to those in the adult, the segmen- 

 tation and the spines being much cleaner and more distinct; they 

 verify in every particular what has already been given for the adult. 



In another developmental stage, 4.5 millimeters long, we find the 

 same general shape and proportion of the various body regions as 

 in the adult. The dorsal plates are now well formed and overlap, so 

 that there are no spaces between them; the third pair are much 

 enlarged and reach to the center of the genital segment ; the sixth 

 segment plate has increased to its normal proportions. But as no 

 pigment has yet appeared the internal anatomy can be seen quite 

 distinctly; in particular the ovaries and oviducts are manifest, and 

 the beginning of the coils in the latter may be distinguished at the 

 posterior end of the genital segment. This absence of pigment, 

 together with the differences in the details of the appendages and 

 dorsal plates make these young females appear like distinct species. 

 And it is probably similar differences which led to the differentiation 

 of hoscii from hicolor by Leach in his original description of the genus, 

 and also to the separation of pallidus from cmnchii by Milne-Edwards 

 in 1840. 



Male. — Carapace elliptical, a little longer than wide, with the lat- 

 eral margins only slightly curved; posterior lobes wdde and bluntly 

 rounded at the tips, extending straight backward; accessory lobes 

 small, much wider than long and attached close to the base of the 

 posterior lobes. Lateral grooves somewhat S-shaped, the curve at 

 the anterior end being much more pronounced than at the posterior 

 end. Eyes prominent and situated far forward. Carapace nar- 

 rowed but little anteriorly; frontal plates wide and prominent, cov- 

 ering nearly the whole of the basal joints of the first antenna^. Free 

 segments diminishing a little in width, but increasing in length from 

 in front backward, their sides plumply rounded ; the second seg- 

 ment filling the entire space between the carapace lobes, the fourth 

 segment wider than the genital segment. Lateral lobes on the sec- 

 ond segment broad and bluntly rounded, reaching back to the poste- 

 rior margin of the third segment. Genital segment subquadrangular, 

 a little wider than long, its sides only slightly rounded; the papillae 

 of the fifth legs small, blunt, and situated far back close to the pos- 

 terior corners, those of the sixth pair larger and more pointed. Abdo- 

 men half as wide as the genital segment, much wider than long, some- 

 what the shape of an hourglass, the sides being reentrant at the 

 groove between the two joints. The terminal joint twice the length 

 of the basal and protruding somewhat at the anus between the bases 

 of the anal lamellae; the latter of about the same length and width, 

 tipped with four large setae, the inner one of wliich is separated a 

 short distance from the others. The first antennge have a long basal 

 joint which is almost entirely concealed beneath the distal end of the 



