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. At c, (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. 1 and 7, ) pass outward and a 

 little downward, and on approaching the apex of the basal joint of 

 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 mass, 

 we have not discovered the muscles moving these parts. We 

 can 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 which 



