NO. 1788. NORTH AMERICAN ERG A8ILIDJE— WILSON. 265 



The Corycseidse, a family of free-swimmers established by Claus in 

 1863, offer the greatest affinity with the Ergasilidse. This resem- 

 blance has already been stated by Vogt (1879, p. 98), and is especially 

 noticeable in the genera Corycseus, Antaria, and LuhbocJcia. 



In superficial view the genus Corycseus looks very much like 

 Ergasilus; there is the same bodily structure, the second antennae are 

 transformed into powerful prehensile organs, the mouth parts are 

 somewhat similar, and even the unpaired eye is small and well con- 

 cealed in the tissues. 



But in spite of t^is seeming likeness the Ergasilidae differ radically 

 from the free-swimmers in both habits and morphology, as can be 

 seen from the account which follows. 



The present paper includes all the genera belonging to the family 

 which have thus far been found in North American waters. On 

 examining the species which have been referred by various authors 

 to the genus Bomolochus, it was soon found that we have among them 

 sufficient differences to warrant the establishing of at least three new 

 genera, Artacolax, Irodes, and Phagus. A diagnosis of Artacolax has 

 already been published.'^ 



A description of the type-species, A. ardeolse, is here added, the 

 diagnoses of the other two genera are given with their distinguishing 

 characteristics, and the different species belonging to each are clearly 

 indicated. There is also presented a comparison of the mouth parts 

 in the two sexes of the three type genera, Ergasilus, Bomolochus, and 

 Tseniacanthus. The mouth parts of the female of each of these 

 genera have already been published, some of them many times, and 

 the large maxillipeds, which are the distinguishing character of the 

 male, have been described and figured. 



But these descriptions have all been isolated and nearly every 

 author has changed the nomenclature of one or more of the mouth 

 parts. The result has been a confusion so great as to make intelligent 

 comparison possible only after long and painstaking study of the 

 published accounts and careful examination of both living and pre- 

 served material. 



To the best of the author's knowledge no collective account of the 

 family as a whole, showing the interrelation of the subfamilies, 

 genera, and species, has hitherto been published. 



ECOLOGY. 



Habits. — The Ergasilidae live almost entirely upon the gill filaments 

 or within the gill cavities of fishes, and this habit has occasioned sev- 

 eral departures from the conditions found existing in the Caligidse. 

 There is about the same difference between the sexes in their 

 morphology, but the difference in habit is considerably greater. 



aProc. U. S. Nat. Mus., vol. 35, p. 433. 



