302 Transactions.—Zoology. 
The internal coxal plates (i. cx. pl.) have the same relations as in P. 
edwardsii, indicating imperfect fusion of the coxocerites : external coxal 
plates are also present. There is, however, no trace of procephalic pro- 
cesses. 
In P. trigonus, another of the Langoustes ordinaires, I am informed by 
Mr. Haswell that there is a prominent squarish rostrum covering the oph- 
. thalmie segment, but that in other respects the resemblance to P. vulgaris 
is very close, there being a well developed stridulating organ, and no 
clasping processes. 
In P. interruptus, as well as in all other Langoustes longicornes which 
I have examined or obtained descriptions of, there is a stridulating organ 
of essentially the same structure as in P. vulgaris. The antennulary sternum 
(figs. 8 and 6, ant. st.) is, however, truncated in front instead of pointed, so 
that no part of it overhangs the articular ends of the antennules, which 
are therefore visible in a view from above. Moreover, the antennulary 
sternum is nearly as broad in its antero-ventral as in its postero-dorsal 
region, so that the basicerites (bc) are kept widely separated, and do not, 
as in all the Langoustes ordinaires, partly hide the bases of the antennules 
when the animal is viewed from above. 
As in P. vulyaris, there is no trace of procephalic processes. The rostrum 
also is completely aborted. a 
The fused pazoodrites present no trace of the median groove mentioned 
plates are absent 
Instead of there baog iko distinct external coxal plates, one for each coxo- 
cerite, there is a single transverse sub-vertical posterior coxal plate (p.cæ. pl) 
consisting of two lamine, an anterior formed by the posterior walls of the 
coxocerites, and a posterior furnished by the epistoma (ep). 
Coming now to the general bearing of these facts, it seems clear, 
to begin with, that the Langoustes ordinaires do ‘not form a natural 
assemblage, since some of the species included in the sub-genus have a 
well-developed rostrum, simple unmodified antennulary sternum, ete., 
while others possess a perfectly formed stridulating organ,—always a 
mark of high specialization, rare under any form in Crustacea,* and in the 
present case of a quite unique type of construction. 
The longicornes on the other hand form a strictly natural group, 
since they all possess the stridulating organ and long antennulary flagella, 
while none have any trace of a rostrum. 
* See Wood-Mason, Proc. Entom. Soc. Lond., Nov. 1877, p. xxvii. 
