712 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxi. 



door skate (Cat. No. 32839, U.S.N.M.), eight females; from honito 

 (Cat. No. 32840, U.S.N.M.), one female. 



This species presents a marked contrast to all the other species thus 

 far known in the entire absence of posterior processes on the genital 

 segment of the female. This segment has instead well rounded poste- 

 rior corners, and there is not a vestige left of the fringe of spines 

 that adorns the margin in other species. In this respect, therefore, 

 the four species form a well-detined series, beginning with difficili^^^ 

 in which the entire genital segment is covered, passing through car- 

 eharlse^ in which there is a heav}^ fringe along the margins, gracilis, 

 in which there are only scattered spines here and there, and ending 

 with (jlahei\ in which the spines have entirely disappeared. 



There is also a direct antithesis in the relative structure of the geni- 

 tal segment in the two sexes between this species and gracilis. In the 

 present species the female has no posterior processes, while the male 

 possesses a pair, although in a considerably reduced form. In gracilis, 

 on the contrary, the female has a pair of stout posterior processes, 

 while the male wholly lacks them. 



Genus DYSGAMUS Steenstrup and Llitken. 



( Founded on males only. ) 



Generic diagnosis. — First three thorax segments united with the 

 head to form a large rounded carapace. Frontal plates distinct and 

 prominent; ej^es large and in contact with each other on the mid-line. 

 Fourth thorax segment free and without dorsal plates. Genital segment 

 small and evenl}- rounded, without posterior lobes or rudimentary legs. 

 Abdomen short, two-jointed, with small anal lamina^. First antennae 

 two- jointed, joints equal in length; second pair as in Alehion. Mouth- 

 tube narrow and conical, longer than in EurypJtorus^ not as long* as in 

 Alehioi). Second maxilh\? simple, broadlv triangular, and slightly 

 curved at the tips; maxillipeds as in Euri/phorus. All four pairs of 

 legs biramose, the rami two-jointed. 



{dysgaijius., Svg, badly, and yduog, wedded, alluding to the fact 

 that no females were found.) 



This genus was founded in 1861 by Steenstrup and Liitken upon ten 

 or more male specimens captured at several diti'erent places in the 

 Atlantic north of the equator. These males were about the same size 

 (3.5 mm. long), and agreed fully in all essential characters. Bassett- 

 Smith, the only other writer who has mentioned the genus, stated in 

 18i)9 that— 



This genus was made by Steenstrup and Liitken from a male only; but in tlie col- 

 lection of the British JNIuseum there are a large number of specimens, some with 

 ext'-rnal ovaries attached, which I have examined and have no d()ul)t of their 

 identity; therefore the genus is allowed to stand. " 



"A systematic Description of Parasitic Copepoda found on Fishes, with an Enu- 

 meration oi tlie known Species, IS'JU. p. -!(^(j. 



