MOUTH-PARTS OF THE SHORE CRAB. 117 
the ea'opodite. The stem of this is a long, narrow, flattened structure, directed 
forwards between the endopodite and the branchiostegite, and bearing at its 
end a flagellum which is directed inwards above the nieius towards the middle 
line. The flagellum consists of a basal joint, and a many-jointed lash, 
curved with the concave side forwards. The exopodite stands at the junction 
of basi-ischium and coxa, and besides being articulated to the former is 
attached by membrane to the latter. 
The ischium is an oblong, roughly rectangular, and very flat joint, which 
makes nearly half the total surface of the limb. It is succeeded by the merus, 
a flat, subquadrate structure, stouter than the ischium and tilted a little 
outwards upon the latter. Owing to its stouter form it has a median face in 
place of an edge, and upon this face, which is hollowed, is set the carpus. 
That joint, with the two which succeed it, forms a subcylindrical, tapering 
palp, which can be stretched out so as to be roughly in line with the axis of 
the basi-ischium and merus, but in the normal [losition is folded back against 
the hollow face of the merus. In this position the palps fill the gap which 
would otherwise be formed by the outward tilting of the merus, and thus 
complete the operculum. 
As has been mentioned, the mode of articulation of the joints is that which 
is found in the legs. At the proximal end of each, the rim of the hard 
cuticle is raised, at two points on opposite sides, into articular processes 
which, bridging over the arthrodial membrane, play against corresponding 
surfaces on the distal rim of the preceding joint ; and these articular 
surfaces are so shaped as to limit the movement of the distal of the two joints 
to a particular direction. Since, however, this plane is a different one in each 
joint, the limb as a whole has a good deal of mobility, though owing to its 
shape and position the third maxilliped is less freelj' movable than the legs. 
I have not thought it necessary to give details of the articulations of the- 
several joints, but particulars of the movements they permit will be found 
below. They are modifications of those of the segments of the legs. 
A remarkable feature of the third maxilliped is the way in which it is 
completely outlined with hairs, set along the edges of its flat surfaces. Most 
of these hairs are feathered in one way or another. They are short where 
the edge is, in the normal position, apposed to some other structure, but lolig 
on that part of tlie anterior (morphologically external) edge of the merus and 
carpus over which the gill-stream flows. Along the median edge of the 
ischium there run on the lower (ventrallj^-facing) side two narrow parallel 
bands of hairs with a naked, convex strip between them. These hairs are 
stout, with a close, stiff feathering on all sides. Tlje actual edge is finely but 
bluntly toothed. On the inner or dorsal (morphologically anterior) side of 
this joint there is a row of hair-tufts near the median edge, and a rather 
sparse band of hairs near the outer edge. The dorsal side of each of the last 
three joints is covered with long, and stiff, serrated bristles. The epipodite 
