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or as I. pelayica of Leach. The latter mistake has hecn previously committed by
the present author; but after having become acquainted with the true /. pelagica
Leach. I now find that it is a very different species, exhibiting a much closer
relationship to I. emarginata,. From this species,
however, it is at once distin-
guished by the very different form of the last segment of the metasome. in which
respect it also differs conspicuously from the North American /. phosphor ea.
Occurrence. The species occurs along the whole Norwegian coast, from
the Christiania Fjord to Vadsd. and is often found in great abundance among
decaying alga?, in depths ranging
from 6 to 20 fathoms. As to its distribution
out of Norway, it is impossible at present to state anything with certainty; but
it is most likely that it also occurs at any rate off the British Isles and in the
Kattegat.
6. Idothea emarginata (Fain-.).
(PI. XXXV, fig. 2.)
Cymothoa emarginata, Fabricius. Entom. Syst. II, p. 508.
Syn: IdotJica extisa, Bosq.
oestrum, Pennant.
Specific Characters. Body oblong oval, scarcely 3 times as long
as it is
broad, and much larger in male than in female. Coxa! plates in female rather
small and not contiguous, in male much larger, and forming on each side a broad
marginal area. Last segment of metasome abruptly truncated at the tip, hind
edge slightly emarginated, with the lateral corners distinctly projecting. Eyes and
superior antennae about as in I. neylecta. Inferior antenna; somewhat less slender,
scarcely reaching to the end of the 2nd segment of mesosome, flagellum not much
longer than the peduncle, and composed
of from 12 to 1(5 articulations. Legs
about as in /. neglccta. Stylet of 2nd pair of pleopoda in male somewhat longer
than in /. neglccta, though not reaching to the end of the inner plate. Uropoda
with the terminal piece slightly emarginated at the tip. Colour rather variable,
sometimes uniformly dark brown, sometimes variegated with larger whitish patches,
which are often confluent along the sides, so as to leave the marginal area?, formed
by the coxal plates, uncoloured. Length of adult female 18 mm.,
of male 30 mm.
Remarks. This species was recorded as early as in the year 1793 by
Fabricius, as Cymothoa emarginata. By earlier British authors (Pennant and
Leach) it was named Idothea oestrum. Though very nearly allied to I. neglecta,
this form is readily distinguished, both from that species and the other Norwegian
Idothese, by the abruptly truncated and emarginated terminal segment of the meta-
some, for which reason it has never been confounded with any of the other species.