12 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



fresh-water species has been discovered within the present area, but 

 this is chiefly due to lack of search, and such a form is likely to 

 appear at any time. 



Family ARGULIDAE 



Genus ARGULUS Miiller, 1785 



Carapace strongly flattened and shield-shaped, its lateral lobes 

 varying much in length ; urosome differing greatly in size and shape 

 but always bilobed posteriorly and furnished with a pair of caudal 

 rami. Basal portion of first antennae flattened and armed with an 

 anterior and a lateral claw; terminal portion cylindrical, 2 or 3 

 segmented. A sheathed sting in front of the mouth, used as a 

 piercing organ; second maxillae transformed into sucking disks, 

 whose margins are supported by a series of chitin rods. Maxillipeds 

 with a chitin plate on the ventral surface of the basal segment, the 

 posterior margin of the plate produced into spines, teeth, or lobes. 

 Basal segments of the fourth legs usually produced into boot-shaped 

 lobes beneath the abdomen. Anterior legs with or without flagella ; 

 basal segments of the posterior pairs in the male sexually modified. 

 Ovary of the female in the posterior portion of the metasome, testes of 

 the male in the urosome. 



KEY TO THE SPECIES (BOTH SEXES) 



1. Carapace orbicular, as wide as long or definitely wider 2 



Carapace elliptical or oval, definitely longer than wide 4 



2. Posterior margin of basal plate of maxillipeds produced into 



3 stout teeth; carapace lobes very short funduli (p. 13) 



Posterior margin of basal plate of maxillipeds without teeth ; 

 carapace lobes relatively longer, sometimes reaching the 

 urosome 3 



3. Urosome definitely longer than wide, its posterior lobes sharply 



pointed; anterior legs without flagella latus (p. 14) 



Urosome definitely wider than long, its posterior lobes broadly 



rounded ; 2 anterior pairs of legs with flagella catostomi (p. 14) 



4. Posterior margin of basal plate of maxillipeds produced into 3 



wide, laminate, and squarely truncated processes laticauda (p. 15) 



Posterior margin of basal plate of maxillipeds produced into 

 3 narrow and sharply pointed teeth 5 



5. Urosome as wide as long, its posterior lobes broadly rounded, 



the sinus between them with parallel sides megalops (p. 16) 



Urosome much longer than wide, its posterior lobes sharply 

 pointed, the sinus between them with divergent sides alosae (p. 17) 



Remarks. — In the final verification of species the form and relative 

 size of the respiratory areas and the detailed structure of the sup- 

 porting rods of the sucking disks on the second maxillae will also 



