. 244 Description of a Species of Caligus. 
attaching itself to the curved process, f (fig. 12,) on each side, 
continues on, and is inserted in the shell. Atc, (fig. 7,) near the 
eyes, we observe the attachment of a pair of muscles which are 
in action when the buccal mass moves; we have not detected 
their insertion, but suppose from their position that they act in 
depressing it. 
‘The internal parts of the mouth which receive distinct mus- 
cles are as follow: the upper lip, the mandibles, and the parts of 
the inner mouth. The upper lip is provided with two pairs of 
retractors which are attached near the centre of the exterior mem- 
brane of the mouth. The interior pair are very slender ; they are 
inserted in a minute process near the extremity of the lip, (fig. 15,) 
and move merely the extremity, giving it the position in fig. 16. 
The exterior pair are four times the width of the interior; they 
are inserted near the middle of the lip and retract this organ 
nearly to the bony arch. 
The mandibles are provided with muscles of extraordinary 
length and power. There are two pairs connected with the same 
slender bony tendon, the one with its extremity, and the other with 
its posterior side. The former, (d, figs. l and 7,) pass outward anda 
little downward, and on approaching the apex of the basal joint 
the third pair of maxillipeds, curve suddenly backward ; they are 
finally inserted in the margin of the shell opposite the articula- 
tion of the head and thorax, after having run over a space equal 
to one half the whole length of the cephalo-thoracic segment. 
The other pair extend obliquely backward and outward under 
the base of the rudimentary feet. Although these organs are 
provided with such remarkable muscles, they are very confined 
in their motions. They occasionally have a vibratory motion 
when the animal is nearly exhausted, and this is the only action 
we have observed. ‘Their position and the form of the adjacent 
parts satisfies us that their extremities cannot be projected out of 
the mouth; and probably they can scarcely reach the opening 
between the lips. 
On account of the thickness of the enveloping membranes, and 
the difficulty of dissecting the internal parts of the buccal 12ass, 
we have not discovered the muscles moving these parts. We 
ean only specify one pair of slender muscles, which are inserted 
in the lateral portions of the process g, (fig. 17.) It is the re 
tractor of these processes, and through them opens the folds whieh 
