298 Transactions.— Zoology. 
An examination of several species of Palinurus has shown that while 
the stridulating organ is present in all the Langoustes longicornes associated 
with long antennulary flagella and obsolete rostrum, there are some Lan- 
goustes ordinaires in which it is well developed, others in which it is wholly 
absent; and further that in the latter group some species have a rostrum 
quite comparable with that of the Astacida, others having one so small as 
to merit special description only from its position. 
I propose to describe, somewhat in detail, the structure of the head in 
P. edwardsii, P. vulgaris and P. interruptus, in order to bring out the points 
of likeness and of difference in three typical forms. 
` In Palinurus edwardsii, one of the common New Zealand species, the 
carapace is produced in front into an upturned rostrum (figs. 1 and 4, 7) 
which is confluent laterally with the large supra-orbital spines (s. or. sp). 
The ventral faces of these latter pass insensibly into the “ epimeral plates” 
(epm. pl.)* which form the posterior walls of the orbits, and are fused exter- 
nally with the anterior border of the carapace and internally with the 
antennulary sternum (ant. st.). This latter is a vertical bar, just wide 
enough below to furnish the articular facets for the antennules (ant. 1’), and 
narrowing to its dorsal end where it becomes bent backwards at a right 
angle (fig. 1) to join with the epimeral plates. The latter, which are con- 
sidered by Huxley as representing antennulary epimera,t bound a trans- 
versely oval area, consisting of uncalcified chitin, and bearing the small 
movable ophthalmic segment (oph.) or pseudo-segment, the middle portion 
of which is calcified, forming the so-called ophthalmic sternum. The epi- 
meral plates are thus united with one another above and below the eye- 
bearing space forming supra-ophthalmic and infra-ophthalmic bars. 
The infra-ophthalmic bar gives off on each side of the middle line a 
pedute process (cl. pr) which extends forwards in contact with, but quite 
free from, both its fellow. of the opposite side and the dorsal or horizontal 
portion of the antennulary sternum. Each of these processes ends in a 
sharp spine and, from its proximal end, sends off an upwardly directed off- 
shoot ending in two small spines, which is so closely applied to the lateral 
surface of the rostrum that the latter appears to be actually squeezed 
between the two clasping processes as they may be conveniently termed 
(cl. pr, figs. 1 and 4). 
These clasping processes appear to have been very imperfectly described 
hitherto.  Milne-Edwards merely says that there are two small spines 
below the base of the rostrum Bo P. lalandii which agrees in all important 
> Huxley, “ The Crayfish,” p. 156, 
+ Is it not more likely that dev tt: represent the ventral region of the unseg- 
mented prestominm? If embryology should answer this question in the affirmative it 
will be — to — of a single prestomial plate consisting of lateral, supra- 
ophthalmic, an portions. 
Wg 
