CALIGOIDEA. 



1351 



Family I. ARGULIDiE. 

 Genus ARGULUS, Juvine. 



In the greater part of the Caligidae, the body clings to the surface 

 upon which it may rest by the margin, even where there are no suc- 

 torial disks for this purpose ; and the enlargement of the third pair of 

 natatories into a broad united plate serves to adapt the animal to this 

 mode of life. Within the cavity beneath the shell the organs may 

 have motion ; and only the fourth or posterior pair of natatories is 

 outside of the cavity, for use when the body is attached. 



In the Arguli, on the contrary, the first pair of feet is a large pair 

 of clinging sucker feet, and the animal attached by them may have 

 the margin free, with the natatory legs in motion to keep up constant 

 currents over the body. The four pairs of natatories are very similar 

 to one another, and the two anterior pairs are the largest. 



The maxilhe are either wholly obsolete, or they are represented by 

 the sheath and its exsertile spiculum, that projects forward from the 

 anterior part of the mouth. This we suspect to be the true relation 

 of this spiculum, an organ not found in other Caligoidea. 



The divisions of the shell or carapax in this genus are well shown 

 in figure 2 a, PI. 94. The same sutures exist as have been described 

 with regard to Caligus, though under some different modifications. 

 The natatory legs in Argulus are arranged by their bases along the 

 sides of the thorax ; while in the Caligidae, they are attached to its 

 under surface. 



Argulus pugettensis. 



Carapax oblongus, ellipticus, pedes omnes tegens. Abdomen oblongum 

 carapace dimidw angustius, postice pro/unde usque ad medium bilo- 

 batum, lobis postice subacutis. Ramus anticus antennce articulo 2do 

 (ultimo) apice uncinato, antice posticeque spinam gerente, 1 mo postice 

 spina armato et posterius splnd alia, exteriusque spina alia ramum 

 posticum antennan gerente. Pedes 2di percrassi, articulo basali denti- 



