Desmption of a Species of Caligus. 231 



membrane, attached by its central portions. Its surface is finely 

 marked with Unes running towards the outer margin ; on the 

 inner margin, these hnes, though possessing the same general 

 direction, freely anastomose. We have often tested the use of 

 these organs by applying the blade of a knife to the front margin 

 below, while the animal was on its back, when in numerous in- 

 stances it has adhered with sufficient force to be lifted from the 

 fish and carried some distance. The membrane of the segment 

 extends beyond the cup and curves around over the base of the 

 antenna adjoining, (fig. 7, PI. IV.) These antennas have no 

 connection with the cup. 



About two fifths of the distance from the cup to the centre of 

 the front margin, we find, on the back, a single slender naked 

 seta. (K, fig. 1.) 



The antennm which terminate laterally this first cephalic seg- 

 ment, (L, fig. 1, and fig. 19, PI. V,) are articulated with it by a 

 joint passing obliquely upwards and inwards, towards the cup. 

 They are two-jointed. The first joint is broad and large at 

 base, and somewhat triangular in form. Its anterior and apical 

 portions are covered with soft ciliated oblong papillee, (fig. 19,) 

 each of which receives a distinct branch of the large nerve that 

 passes to this organ. They shrink up and become obliterated on 

 drying, and in this respect difier from similar appendages to other 

 parts of the body, and even from the naked setae that terminate 

 the apical joint of the antennae. This apical joint is nearly cylin- 

 drical in form and is about two thirds the length of the basal. 

 The terminal setee are of two kinds ; those at the inferior part of 

 the apex are slender and acute, and those at the superior part, 

 short and somewhat obtuse. A single naked slender seta, usually 

 curved or bent, may be observed near the middle of the posterior 

 margin of this joint. 



2. Posterior Cephalic Segment. — The mouth, (figs. 1 and 12,) 

 is situated in an oblong mass, which lies entirely external, along 

 the under surface of the body, near the centre of the posterior 

 cephalic segment. This buccal mass is in part a hollow organ, 

 (fig. 12, PI. IV,) bounded above and below by distinct membranes, 

 a portion of which represent the upper and under lip. It has a 

 lunate opening between the approximating lips, (a a and b, fig. 

 12,) and contains a pair of strong mandibles and other organs, 

 which we shall soon describe. It is articulated with the cephalic 

 segment by its broad posterior portion. 



