MOUTH-PARTS OJF THE SHORE CRAB. 121 
endite, which projects towards the mouthj is being drawn away from the 
latter. When the smaller endite comes forward into the mouth the larger 
endite moves away from it. 
4. The Maxilla (Second Mamlla) is a verj' broad limb, flattened in its 
distal parts, but with a swollen nucleus representing the main p;irt of the 
protopodite. This region bears on the outer side the large, quadrant-shaped, 
slanting exopodite or scaphognathite, distally the roughly-ogival, peaked 
endopodite, and internally the two cleft lobes, representing four endites^ 
which characterise tlie maxilla of the Decapoda. I have already (5) sug- 
gested that the first of these endites belongs to a precoxal segment of the limb, 
the second to the coxii, and the third and fourth to the basis. The first cleft 
lobe is in Careinus reduced to a pair of narrow ribbons. The limb is covered 
with a delicate cuticle, thickened in places to form certain sderites. Across 
the protopodite there runs on the ventral (morphologically posterior) face, 
from the junction between the cleft lobes to the base of the limb at its outer 
side, a raised ridge, strengthened by a sclerite which probably represents the 
coxa. At its outer end this abuts upon a longitudinal piece which caps the 
side of the swollen nucleus of the limb, and which is sutured to, but not 
definitely articulated with, the epimerite. More distally, the protopodite is 
crossed by an irregular M. shaped, transverse ridge, strengthened by two 
sclerites, each of the form of an inverted V, which are hinged to one another 
where they meet at the apex of the Wl. This appears to represent the distal 
limit of the basis. On the dorsal (anterior) face of the limb a longitudinal 
ridge, strengthened by a sclerite which roughlj' corresponds in position to 
the outer member of the M on the opposite face of the appendage, partly 
separates exopodite from protopodite. On the anterior face of the scaplw- 
gnatldte are two sheets of stout cuticle, with thickened edges, which support 
it and provide for the insertion of the accessory muscles. The maxilla is 
seated upon the membranous body-wall, in front of the sternum, upon which 
it does not abut. It is attached by membrane only, except at its outer end, 
where, as mentioned above, one of its sclerites is joined by a flexible suture 
to the epimeral region. 
The liairs which in a prawn fringe the whole edge of the scaphognathite 
are here found at its anterior and posterior returning edges only. As in the 
prawn, they are feathered. The endopodite is fringed with long, silky hairs, 
but these are feathered only at the base of the outer edge. The ends of the 
cleft lobes bear relatively short, and, for the most part, simple hairs. 
The swollen base of the maxilla harbours a complicated and relatively 
powerful musculature. According to Pearson (13), \vhose account is, I think, 
applicable to Careinus, there are in Cancer two extensors and two flexors of 
the coxa, and four " extensors " and four " flexors " of the scaphognathite. 
It would perhaps be preferable to call these muscles abductors and adductors 
respectively, since they draw the limb downwards from the side of 
