Parxer.—On the Structure of the Head in Palinurus. 299 
respects with P. edwardsii), and the same statement is made by Miers* and 
by Haswell.t The processes are perfectly distinct from the rostrum, either 
being removable without injury to the other, and clearly belong to the 
epimeral plates, so that if the latter are, as Huxley supposes, antennulary 
epimera, the clasping processes are to be looked upon as epimeral—or pos- 
sibly as partly sternal and partly epimeral—outgrowths of the antennulary 
segment, 
The true relations of the rostrum are very imperfectly seen in an external 
view: owing partly to the presence of the clasping processes which form an 
apparent proximal boundary to it, partly to the fact that on its dorsal sur- 
face it widens out suddenly and becomes confluent with the supra-orbital 
spines, it appears externally as a very small structure, hardly larger indeed 
than the clasping processes (fig. 4). But a longitudinal section (fig. 1) 
shows that it is really a structure of considerable size, being continued 
backwards some distance behind the clasping processes, and a short distance 
behind the ophthalmic segment where its ventral plate turns sharply forward 
. and becomes continuous with the supra-ophthalmic bar of the epimeral 
plates. 
A short distance on each side of the middle line the supra-ophthalmic 
bar is produced into a small hollow procephalic process (fig. 1, pre. p.) which 
passes backwards, upwards, and outwards into the interior of the head 
quite like the homologous structure in Astacus and Homarus, from which it 
differs only in its small size: in a moderate sized specimen (8 or 9 inches) 
of P. edwardsii it is only about +; inch in length. | 
The proximal segments (coxocerites) of the antenne are, as in other 
species of the genus, fused with the carapace, so that the apparently proxi- 
mal segment is really the second or basicerite (bc); of the coxocerites only 
the ventral portions are left, their lateral and dorsal regions being as it 
were squeezed out of existence by the immense development of the free 
portions of the antenne, the articular cavities for which are thus bounded 
above by the epimeral plates, internally by the antennulary sternum, exter- 
nally by the anterior borders of the carapace, and only below by the coxo- 
cerites. The fused coxocerites thus come to occupy the position of the 
epistoma of Astacus,j from which, however, they are at once distinguished 
by bearing the renal apertures. Posteriorly they are continued in the 
middle line into a projecting transverse bar (ep) which gives attachment to 
the labrum, furnishes the antero-internal articular facets for the mandibles, 
and apparently is the much reduced representative of the true epistoma. 
*Cat. of the Stalk- and Sessile-eyed Crustacea of N.Z., 1876. 
{Cat. of the Australian Stalk- and Sessile-eyed Crustacea, 1882. 
t Huxley, ‘ The Crayfish,” p. 155. 
