COPEPO'BA 



349 



4-jointed and modified to form a pair of large hooks for prehensile pur- 

 poses; female carries a pair of long- q^^<^ sacs and is parasitic, usually on 

 the gills of fresh-water fishes: about 10 ge- 

 nera and 85 species; about 15 species known 

 in America. 



Ergasiltjs von Nordmann. Cephalo- 

 thorax pear-shaped, fifth pair of legs rudi- 

 mentary': several species. 



E. versicolor C. B. Wilson (Fig. 550). 

 Length 1.5 mm, : parasitic on the gills of the 

 common bullhead and three kinds of catfish. 



Family 7. CALIGIDAE.* 



Body wide and flat, the segmentation 

 being more or less obliterated and the female 

 being larger than the male; first antennae 

 short, with 2 to 3 joints; second antennae in 

 form of short hooks; mouth parts form a 

 suctorial beak; first 4 pairs of legs usually 

 biramose and facilitate rapid swimming; 



fifth pair reduced or ^^S- 



wanting; 2 long egg 



sacs with the eggs in a single row in each : about 



35 genera and 200 species, which are parasitic 



externally on fishes. 



Key to the genera of Caligidae here described : 



fli A pair of suckers at front end of bodj'. .1. Caligus 

 Qz No suckers present 2. Lepeopiitheirus 



1. Caligus 0. F. Miiller. First and fourth 

 pairs of legs uniramose, second and third bira- 

 mose ; body composed of 4 parts, a cephalothorax, 

 a thorax, a genital segment, and an abdomen; a 

 pair of suckers at the base of the first antennae : 

 17 American species. 



C. rapax Milne-Edwards (Fig. 551). Free 

 thoracic segment small and narrower than the 

 genital segment, which in the female is about 

 twice as wide as the abdomen; length of female 

 about 6 mm. : the commonest species, occur- 



5 5 — Erqasi In s v ersi- 

 color (Wilson). 



Fig. 551 — Caligus rapax 



(Wilson). 1, sucker ; 



2, egg sac. 



* See "North Am. Parasitic Copepods Belonging to the Family Caligidae." etc.. by 

 C. B. Wilson, Proc. U. S. Nat. Mus., Vol. 28, p. 479, 1905 ; Vol. 31, p. 669, 1907 ; Vol. 

 33, p. 323, 1908. 



