COPEPO-DA 



349 



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

 poses; female carries a pair of long egg 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. 



ERGASILUS 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 



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 : 



(ii A pair of suckers at front end of body. .1. CALIGUS 

 o 2 No suckers present 2. LEPEOPHTHEIEUS 



1. CALIGTJS 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- 



Fig. 550 Ergasilus versi- 

 color (Wilson). 



Fig. 551 C aligns 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, 



