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Description of a Species of Caligus. 231 
membrane, attached by its central portions. Its surface is finely 
marked with lines running towards the outer margin; on the 
inner margin, these lines, 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, Pl. IV.) These antenne 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 antenne which terminate laterally this first cephalic seg- 
ment, (L, fig. 1, and fig. 19, Pl. V,) are articulated with it by a 
joint passing obliguibr maitechisli 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 apiad 
portions are covered with soft ciliated oblong papille, (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 differ from similar appendages to other 
parts of the body, and even from the naked sete that terminate 
the apical joint of the antenne. This apical joint is nearly cylin- 
drical in form and is about two thirds the length of the basal. 
The terminal sete 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, Pl. 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, (aa 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. 
