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Scientific Memoirs by

embrace the ridge, and while the convexity of the ridge has a dead-polished
surface the concavity of the lobe is finely striated; and the sound is made by the
friction of the two opposed surfaces.

       It is interesting to observe that this organ of defence—for both sexes have
the apparatus and use it freely when captured—is in part formed by the anten-
næ, which are the appendages used in offence by Palinurus who has no nippers.

       The same connexion of functions is illustrated by the Peneus above referred
to, in whom the stridulating telson is also a powerful weapon of offence; and by
Gonodactylus, Alpheus, Matuta, and Ocypoda, in all of which both sexes are alike.

       Matuta.— The Indian species of this genus are four in number, and in all of
them, as is well known, a strepitating mechanism is found in both sexes. The
most important part of the apparatus is situated at the upper part of the inner
surface of the " palm " of the nippers, and consists of two patches—one oval, the
other long and narrow—of fine parallel ridges, forming a file-like surface.
These files can be rubbed either against the rough lower edge of the orbit or
against a ridge, on the pterygostomian region, to the causation of sound. A
little reticulated facet, which is present in all the species, except M. lunaris, on
the outer surface of the orbital angle, may perhaps participate.

       I have heard Matuta lunaris and Matuta miersii stridulate angrily when
touched.

       Ocypoda.— The crepitating apparatus of the Ocypode crabs has been fre-
quently described. It is found in every species but one, although its details of
structure have specific differences. It consists of a broad file-like band of
teeth and fine ridges, placed across the far end of the inner surface of the " palm "
of the enlarged cheliped, the whole being more or less fringed with, or embedded
in, short hair. This can be scraped across a series of tubercles, or a definite
ridge, running along the inner surface of the ischiopodite of the same cheliped,
much as a man might rub his breast with the palm of his hand.

       Probably all the Ocypodes that possess it make use of this fiddle and bow,
but I myself have only heard it at work in Ocypoda macrocera, and then only
after prolonged attention to the species to this end.

       As mentioned in another section, the Ocypodes live in large warrens near
high-water mark, each individual having its own particular burrow, into which it
retreats at the slightest alarm.

        I carefully observed Ocypoda ceratophthalma for three surveying seasons
before I heard it stridulate, the noise being then the outcome of my having cut
off a crab from its own burrow and compelled it to intrude into the burrow of
one of its fellows. The intruder crouched down at the entrance of the burrow,