NO. 2063. NORTH AMERICAN PARASITIC C0PEP0D8— WILSON. 577 



the surface on which the so-called swimming legs appear, and their 

 presence in such a position is difficult to understand. 



The antennules or first antennae. — These are attached to the frontal 

 margin of the head, between the bases of the second antennae and the 

 proboscis, often somewhat more on the ventral than on the dorsal 

 surface, but usually the most dorsal of all the appendages. 



In Tracheliastes and Basanistes they arise on the dorsal surface of 

 the head and are not turned downward and forward as in the other 

 genera. They are extremely simple and are made up of tln-ee or four 

 jomts,more or less distinctly separated. Thebasal joint is the thickest 

 and is fused with the head, the other joints are cylindrical and taper 

 distally, and the terminal joint is armed with a few short nonplumose 

 setae or spines. 



The antennae, or second pair. — ^These are characteristically modified 

 in the present family. They arise from what may be termed the 

 anterior corners of the head on either side ; they are flattened laterally 

 and turned forward and inward along the anterior margin of the head, 

 imtil in some species their tips meet or even overlap at the midline. 

 They are made up of a thick basipod and two short rami, one dorsal 

 and one ventral; the endopod or dorsal ramus is usually much larger 

 than the exopod, is thick and fleshy, unsegmented, and bluntly 

 rounded at the tip, where it is armed with a few short spines or teeth 

 (Charopinus, Achtheres, Brachiella), sometimes with olfactory cyhn- 

 ders {Clavella, sp.) or even with claws (Lernaeopoda, sp.) . The exopod 

 is slender and cyUndrical, usually two-jointed, and is tipped with 

 tactile hairs, olfactory cyhnders, or a chitin claw. 



The claw is more common in the male, where these antennae serve 

 as attachment organs, where they have a stout musculature, and 

 where the claw sometimes shuts down against the terminal joint and 

 is chelate in function. In rare instances in the female the two rami 

 are arranged like the jaws of a chela and must function as a grasping 

 organ (Lernaeopodina longimana and Charopinus ramosus). 



The mouth tube or prohoscis. — This is attached between the bases of 

 the second antennae, is conical in shape, and is directed downward and 

 forward against the skin of the host. It is composed of an upper and 

 an under hp ; each side of the latter is spUt into two lamellae, between 

 which is fastened the corresponding side of the former, so that the two 

 lips are loosely joined along their lateral edges to form a closed tube. 

 But they are not held together very firmly, and it is an easy matter to 

 separate them with a needle (fig. 2). At the base of these lateral 

 seams both hps are cut away a httle to form a three-cornered opening 

 through which the mandible projects into the interior of the tube. 



The under hp is somewhat larger than the upper and more spoon- 

 shaped, so that its anterior end, around the mouth opening, is curved 

 like a horseshoe. The upper hp is flatter, broadened at the base, and 

 34843°— Proc.N.M.vol.47— 14 37 



