426 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxm. 



concealed. If it be compared with the figure here given (Plate 

 XXXIV, fig. 205) of a young female alatus, its identity is manifest 

 at once. 



Beneden made the same mistake in 1892 with his Nogagus angus- 

 tatus, which is shown on page 431 to be a Nesippus. He described 

 a young female as a male of the species. Ki'oyer in 1863 erred in 

 another direction. He found a young female Nesippus and a Nogagus 

 latreillii upon the same fish and described the two as the male and 

 female of Nogagus latreillii (see p. 441). 



The true male of the genus has never before been described. This 

 is probably due to the fact that the male staj^s on the outside sur- 

 face of the shark's body, in company, usually, with one or both sexes 

 of some of the other genera. The young female stays in the same 

 place, or in the gill cavity close to the surface, until after union with 

 the male, which takes place very early in development, as in all 

 the parasitic copepods, and then she crawls down into the shark's 

 thi-oat out of sight and remains there fastened to the inside of the 

 gill arches. In the examination of several scores of sharks by the 

 present author, a male has never yet been found in company with 

 one of these mature females in the shark's throat, but many have been 

 taken on the fms and in the gill cavity, some of which were in union 

 with young females. 



It was difficult, therefore, to locate the two sexes at first and re- 

 quired long continued search before they were definitely determined. 

 This leaves Heller's two species, orientalis and cnjpturus, composed 

 of females alone with the male unknown, while Dana's curticaudis and 

 Steenstrup and Liitken's horealis are known only in the male sex. 

 Dana's species was taken "from the body of a shark, northeast of 

 New Zealand," while both of Heller's species came from Java. These 

 localities are near enough together, especially when we remember that 

 the hosts are large sharks, for it to be at least possible that future 

 investigation will find two of the species more closely related. 



NESIPPUS ALATUS Wilson. 



Plates XXXIV and XXXV. 



Nesippus alatus Wilson, 1905, p. 130. 



Nogagus tenax{'^) Steenstrup and Lutken, 1861, p. 388, pi. x, fig. 20. 



Female. — Carapace transversely elliptical, the width once and three- 

 quarters the length; frontal plates distinct, and, together with a por- 

 tion of the cephalic area, projecting in a half circle from the anterior 

 margin; deeply incised at the center. Posterior lobes short, scarcely 

 overlapping the lateral lobes of the second and third segments; 

 thoracic area quadrilateral, arched a little above the surrounding sur- 

 face; lateral areas ver}^ wide; cephalic area small. Eye distinctly 

 tripartite, appearing as tliree separate circular lenses arranged in a tri- 



