Description of a Species of Caligus. 245 
close the esophagus, by means of a tendon inserted in the lastge 
extremity of these folds. 
The basal joint of the first pair of macillipeds has but little 
motion. There are two short muscles, elevating or depressing 
the extremities of this joint, which we may consider a flexor and 
an extensor. ‘The flexor, which is inserted near the interior ex- 
tremity, is directed backward and a little outward to its attach- 
ment to the lower shell, exterior to the base of the following pair 
of feet. The extensor is inserted at the posterior margin of the 
joint, and extends obliquely inward, approaching the attachment 
of the flexor. In the female these muscles have nearly the same 
position as in the male (fig. 18a;) the flexor is inserted near the 
spine on this jot. The united action of these muscles draws the 
anterior margin of this joint from the shell. To oppose this mo- 
tion there is a large muscle inserted near this margin and extend- 
ing one side below the eyes, (e, fig. 7,) where it is attached to the 
back shell. 
The extensor of the second joint of this pair of legs is a long 
broad muscle attached to the shell above the large curved spine, 
(f, fig. 7.) There is a small flexor of this joint, attached to the 
posterior apex of the basal joint. 
The rudimentary feet, or second pair, are provided with but 
few small muscles, requiring no remarks. 
The third pair are remarkable for having as various motions as 
could be afforded by a ball and socket joint. This arises from 
their insertion on a fleshy prominence, composed probably of the 
rudiments of the small basal joints in the corresponding organs of 
the higher crustacea. 'To produce these various motions, each 
leg is provided with five muscles radiating from the base, some of 
which are of very peculiar form. Four of these muscles are in- 
serted into the base of the first joint and one along its posterior 
margin. The latter appears to be attached to the back near the 
median line, a short distance behind the eyes, (g, fig. 7.) Of the 
remaining muscles, two pass forward and outward, (h, i fig. 1 
and fig. 7,) one directly outward, and the fourth, (k, fig. 7,) back- 
ward and outward. 'The most. anterior (h) is a slender muscle, 
attached just exterior to the base of the first pair of maxillipeds. 
The second (i, fig. 1 and fig. 7) is composed of two parts in- 
serted into the same tendon. These parts continue together 
through half their length, then separate, and soon after each di- 
i 
