NO. 1573. PARASITIC COFEPODS— WILSON. 465 



Male. — A fixed form like that of .tlie female and incapable of loco- 

 motion; carapace and thorax segments similar to those of the female, 

 the dorsal plates of the fourth segment being reduced in size. Gen- 

 ital segment also much smaller, with the abdomen partially visible 

 beyond its posterior margin; abdomen without wings in all the 

 genera. Second antenmie and second maxillipeds with stout prehen- 

 sile claws; all the feet biramose, rami as in the female, except that 

 those of the fourth pair are not much enlarged in any genus but 

 Orthagoriscicola; rami of first three pairs with plumose setae in Phi- 

 lorthragoriscus and Luetkenia, the fourth pair and all the rami in 

 other genera without them. 



Chalimus attached by two broad , ribbon-like frontal iilaments very 

 short and parallel. 



KEY TO THE GENERA. 



a, Females, third dorsal plates of medium size, covering quite a portion of the gen- 

 ital segment; the latter as large as the carapace or much larger h. 



a, Males, third dorsal plates small, overlapping the genital segment Init little; the 



latter much smaller than the carapace e. 



b, Abdomen with broad wings between which and the genital segment the long 

 egg-strings are entirely concealed; genital segment much larger than the 



carapace c 



b, Abdomen without wings; egg-strings long and entirely visible; genital seg- 

 ment a little smaller than the carapace d. 



c, First antennae two-jointed, not prominent; second antennae hidden; posterior 

 border of carapace deeply concave; margin of carapace and dorsal plates 



smooth Cecrops Leach, 1816, p. 466. 



c. First antennae three-jointed, prominent; second pair projecting beyond the 

 carapace margin; posterior border of carapace slightly concave; margin of car- 

 apace and dorsal plates coarsely toothed ... Orf/^agfomaVo/a Poche, 1902, p. 472. 

 d, Margins of the carapace and dorsal plates finely toothed; third dorsal plates 

 covering three-fifths of the genital segment; rami of first swimming legs 



normally developed Philorlhragoriscus Horst, 1897, p. 478. 



d, Margins of carapace and dorsal plates smooth; third plates scarcely over- 

 lapping the genital segment; endopod of first legs very rudimentary (male) 



or entirely lacking (female) Luetkenia Claus, 1864, p. 464. 



e. Third dorsal plates relatively as large as in the female; grooving of the carapace 



nearly invisilile; abdomen almost or c^uite concealed /. 



e, Third dorsal plates very much reduced ; groovingof the carapace distinct; abdo- 

 men largely visible (j- 



f, First antennae two-jointed; second and third thorax segments fused inter 

 se and furnished with a pair of broad lateral plates, concealed beneath the 

 carapace; abdomen also entirely concealed . . . Cecrops Leach, 1816, p. 466. 

 /, First antennae three-jointed; second and third thorax segments distinct 

 and entirely visible, without plates; abdomen partly visilile; margins of 

 plates on fourth and genital segments coarsely toothed. 



Orthagoriscicola Poche, 1902, p. 472. 

 g, Second antennae much enlarged and projecting beyond the carapace; first dor- 

 sal plates large; genital segment with large spines at the posterior corners; first 



swimming legs normally developed Philorthragoriscus Horst, 1897, p. 478. 



g, Second antennae smaller and concealed; all the dorsal plates very small; geni- 

 tal segment with smoothly rounded posterior corners; endopod of first swim- 

 ming legs scarcely visible Luetkenia Claus, 1864, p. 464. 



Proc. N. M. vol. xxxiii— 07 30 



