NO. 1573. PARASITIC COPEPOD&— WILSON. 345 



SYSTEMATIC DISCUSSION. 



The first thorax segment only fused with the head, the others free; 

 sexes quite dissimilar. 



Female. — Carapace short and well rounded; frontal plates distinct. 

 Eyes three in number, fused on the median line, the lenses arranged 

 in the form of a triangle. One or more of the free thorax segments 

 furnished with paired dorsal plates; genital segment enlarged and 

 often covered with similar dorsal plates. Body stiff in consequence 

 of these plates and not capable of much motion. Abdomen elongate, 

 often with lateral processes; anal laminae large and broad, with stout 

 plumose seta^. Eggs numerous, uniseriate, antl borne in straight 

 cases, visible for their entire length and usually much longer than 

 the body. Mouth-tube elongate and tapering to a sharp point; first 

 maxillas lacking, second pair simple flattened lamina?, tipped with 

 short claws. Second maxillipeds massive and nodose. All four pairs 

 of legs biramose; some or all of them lamellar and destitute of 

 plumose setae. 



Male. — A typical Nogaus form. Carapace more elongate than 

 that of the female and produced posteriorly into better defined lateral 

 lo])es. Free segments all well separated, of about the same length, 

 but diminishing regularly in width, and none of them furnished with 

 dorsal plates. Genital segment also without dorsal plates and en- 

 larged but little. Abdomen two-jointed; anal laminas large and 

 foliaceous, furnished with long and stout plumose setae. The adult 

 males are as free swimmers as any of the Caliginae and move about 

 with as much ease over their host's body, thus affording a marked 

 contrast to the fixed females. The young are attached by two broad 

 and ribbon-like filaments, placed side by side and very short. 



KEY TO THE GENERA. 



a. Females, first thorax legs uniraiuose, the other pairs Itiramose; only two pairs 



of dorsal plates Pholidojms, new genus name, p. 347. 



a. Females, all four jaairs of legs biramose; one, three, or four, but never two, pairs 



of dorsal plates; abdomen one-jointed and wholly concealed in dorsal view, b, 



a. Males, all four pairs of legs biramose and armed with long plumose setffi; no 



dorsal plates; abdomen one or two jointed, wholly visible g. 



b. Rami of all the legs with the same number of joints, and all armed with 



long plumose sette c. 



b. Rami differing in the number of joints, and some or all of them destitute 



of plumose setae, or even spines _ d. 



c. Four pairs of dorsal plates; first and third pairs median, second and fourth 

 pairs lateral; fourth pair on the genital segment, elongate, narrow, partly 



fused .Lepimarrus Hesse, 1883, p. 348. 



c. A single pair of small dorsal plates on the fourth segment; genital segment 

 elongate, with a deep posterior incision; al)domen unsegmented. 



Demoleus Heller, 18(j5, p. 349. 



