MANUAL OF NATURAL HISTORY. 307 



VI. CLASS. — Fish-Parasites (Epizoa). 



Animal parasitic on the skin or in the gills and 

 mouths of fishes ; mouth tubular, prolonged in the 

 form of a sucker, armed with styliform mandibles ; 

 legs natatory or rudimentary. 



I. ORDER. — Shield-headed Fish-Parasites 



(Peltocephala). 

 Head clypeiform, furnished in front with frontal 

 laminae, and bearing on each side flattened antennae 

 formed of two joints ; thorax jointed ; abdomen 

 ending in ciliated fins ; feet four pairs, entirely na- 

 tatory. 



1. Fajviily. — Fresh-water Fish-Parasites (Argu- 



lidae). Dorsal surface of thorax without 

 lamellar appendages ; foot-jaws of second 

 pair replaced by large suckers ; legs lamel- 

 lar, horizontal, and ciliated ; abdomen with 

 caudal lamellae on the under surface. 



2. Family. — Fish - Parasites proper (Caligidae). 



Dorsal surface of thorax without lamellar 

 appendages ; no suckers in place of second 

 pair of foot-jaws ; legs with long silky 

 plumes ; abdomen ending in two small pos- 

 terior laminae. 



3. Family. — Elytroid Fish-Parasites (Pandaridae). 



Dorsal surface of thorax with lamellar ap- 

 pendages or elytroids ; no suckers in place 

 of second pair of foot-jaws ; legs rarely fur- 

 nished with silky tufts ; terminal fins lobu- 

 lar and foliaceous. 



