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54
2. Gnathia dentata,
(PI. XXII. fig. 2.)
G-. 0. Sars.
dentatus, G. O. Sars, Umlersegelser oyer Hardangerfjordens Fauna I. Chr. Vid. Selsk.
Forh. 1871, p. 32.
Specific Characters. Male: Body comparatively more elongated
than in
(1. nui.rUlaris. and less clavate in form, with the posterior division of mesosome
scairt-ly narrower than the anterior, both being defined by a very conspicuous
constriction. Cephalosome rounded quadrangular, with the supra-ocular processes
rather prominent, dorsal face, behind the anterior excavation, evenly convex,
without any areolation, but, like the first 2 segments of mesosome,
clothed all over
with very small spikes and stiff hairs. Posterior division of mesosome quite
smooth, middle segment divided dorsally into 2 areolse, separated by
a rather
broad membranous space. Metasome comparatively shorter and broader than in
G. maxillaris, with the epimera triangularly produced. Eyes well developed. Inferior
antennae with the last joint of the peduncle rather large, subfusiform. Mandibles much
smaller than in G, ma.r/Unris, with a very conspicuous tooth-like projection in the
middle of the outer edge, tip slightly incurved, acuminate, inner edge distinctly crenu-
lated, and obtusely produced near the base. Pereiopoda without any distinct tubercles
inside the outer joints. Pleopoda well developed, natatory. Terminal segment of meta-
some triangular and rather broad. Uropoda with the rami well-developed, foliaceous.
Sexual process very long, pointing anteriorly. Colour greyish white.- Female:
Body rather narrow with the 3 posterior pedigerous segments completely coalesced,
and forming together an oblong, subcylindric division, more than 4 times as long
as that preceding it. Cephalosome very small, twice as broad as it is long, front
hut very slightly produced, minutely bidentate at the tip. Pleopoda, as in the
male, natatory. Colour yellowish white, mottled with scattered reddish specks.
Length
in both sexes 4 mm.
Remarks. The present species may be easily distinguished from the pre-
ceding one, in the adult state of both sexes, whereas the larvse are of a very
similar appearance to those of G. ma,r'iUr'ts. In the male,
of the mandibles and the non-areolated dorsal face of the head may
the structure
serve as
easily recognizable distinguishing marks; in the female, the very different shape of
the Cephalosome, and the complete fusion of the posterior dilated segments of
the mesosome.
Occurrence. This form was first observed by the present author in the
inner part of the Hardanger Fjord, and has subsequently been found occasionally
in .-i few
other places on the west coast of Norway, as also in the Trondhjem
Kjord. It generally occurs on a stony bottom among Hydroida, the depth vary-
ing from 20 to 50 fathoms. In habits it exactly agrees with the type species.