308 MANUAL OF NATURAL HISTORY. 



II. ORDER. — Thick-headed Fish-Parasites 

 (Pachycephala). 



Head thick, obtuse in front, with two slender, 

 cylindrical, setaceous, many-jointed antennae arising 

 from under its anterior margin ; legs not natatory ; 

 thorax jointed. 



1. Family. — Tufted Fish -Parasites (Ergasilidae). 



Head large ; body pyriform, abdomen coni- 

 cal, ringed, ending in two long tufted ap- 

 pendages ; anterior foot -jaws in form of 

 cylindric appendages ending in a two-jointed 

 hook, posterior foot-jaws not cheliform. 



2. Family. — Pincer-bearing Fish-Parasites (Diche- 



lestiidse). Head small ; body elongated ; ab- 

 domen rudimentary ; legs slightly developed ; 

 first pair of foot-jaws cylindrical, ending in a 

 curved hook, posterior foot-jaws sub-cheH- 

 form. 



III. ORDER. — Lernean Fish-Parasites (Lerneida). 



Thorax not jointed ; legs always rudimentary ; 

 foot-jaws undeveloped. 



1. Family. — Hook -jawed Lerneans (Chondracan- 



thidse). Foot jaws in form of strong hooks ; 

 antennae generally distinct ; thoracic mem- 

 bers of many pairs, free, rudimentary. 



2. Family. — Brachial - Lerneans (Lerneopodidse). 



Thorax with large, brachiform appendages 

 united at the ends ; usually with antennae, 

 and at least two pairs of curved jaw-feet. 





