498 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



first antennae (an', fig. 4). These latter are attached to the frontal 

 margin of the carapace and project sidewise from the bod} 7 . Each is 

 made up of three joints; the basal joint is the largest and is in the form 

 of a lamina or plate, which bears a lunule on its margin. The median 

 joint is larger than the terminal and bears tactile plumose setse on its 

 anterior and outer margins. The terminal joint is usually more or 



less club-shaped and furnished 

 with short and sharp spines at 

 and near its tip. These antenna? 

 should be very highty sensitive, 

 if their innervation is any cri- 

 terion, for a large nerve enters 

 each from the supra-cesophageal 

 ganglion, and, dividing and sub- 

 dividing, sends a branch to the 

 sucking disk of the basal joint, 

 to each plumose seta of the 

 median joint, and each spine of 

 the distal joint. 



The second antenna? (an") are 

 attached to the ventral surface 

 just posterior to the bases of the 

 first. They are each two-jointed, 

 the basal joint being short and 

 stout and plentifully supplied 

 with strong muscles. The apical 

 joint is modified into a stout pre- 

 hensile claw, which fits into a 

 cup or socket hollowed out of 

 the ventral surface of the cara- 

 pace near its front margin. In 

 the genera under discussion 

 these antenna? have become en- 

 tirely prehensile in function, 

 and, with the second maxillipeds, 

 they are the chief organs of at- 

 tachment in places where the 

 skin is accessible (fig. 5). 

 The mandibles are wholly inclosed within the mouth tube; they are 

 very slender, stylet-shaped and usually four-jointed. 



The apical joints are visible through the mouth opening; they curve 

 in toward each other and are either serrated or crenated along their 

 inner edges, the number of teeth being twelve to sixteen. 



In Lepeophthevms the outer margins are smooth, but in Caligus 

 they are sometimes cut into very small acute teeth, eighteen to 



Fig. 4a. — Ventral surface and appendages of an 



ADULT FEMALE LEPEOPHTHEIRUS EDWARDSI. an'., 

 FIRST ANTENNiE; an"., SECOND ANTENNAE; f., FURCA; 



m., mouth; mx'., first maxillae; mx"., second 

 maxilla; mxp'., first maxillipeds; mxp"., sec- 

 ond maxillipeds; 1, 2, 3, AND 4, swimming legs. 



