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81
viz., laem marina, it is best to adopt the name baltica proposed by Pallas,
which name undoubtedly refers to the present species. The name under which
this form lias more generally been recorded, is that of Idothca tricuspidata Des-
merest; but the Pallas' name ought certainly to be preferred as the much older
one. It is the largest of the Norwegian Idothese, and easily recognizable in both
sexes by the form of the terminal segment of the metasome,
which I have found
to be pretty constant even in very young specimens. As is the case with other
species of the genus, the form of the body in fully grown, ovigerous females
slightly differs from that in male specimens, in so far as the greatest width
occurs somewhat farther forward, or across the middle of the incubatory pouch.
The male is also considerably larger than the female, and has the coxal plates
c< imparatively broader.
Occurrence. The species occurs rather frequently along the whole Nor-
wegian coast, from the Christiania Fjord at least to Tromso, in comparatively
shallow water among algpe. Though being more generally of a rather stationary
habit, slowly creeping about on the bottom, the animal is by
no means devoid of
swimming power. At times it may even be seen to move rather rapidly through
the water. In doing so, the valvular uropoda are found to be widely separated,
so as to allow the free play of the anterior pairs of pleopoda, by the strokes of
which, the animal is propelled through the water.
Distribution. British Isles (Sp. Bate), Kattegat (Meinert), Baltic (Pallas),
Dutch coast (Hoek), coast of France (Bonnier), Mediterranean (Heller), Black Sea
(Czerniawsky), Atlantic coast of North America (Harger).
2. Idothea pelagica, Leach.
(PI. xxxur.)
Idotltea -pday'ica, Leach, Trans. Linn. Soc. Vul. XI, p. 3B"i.
Syn: Idothca brcricorms, Eatliko.
torosa, Eaihke.
Specific Characters. Body comparatively short and stout, being scarcely
3 times as long as it is broad, with the segments very sharply marked off from
each other. Coxal plates in both sexes comparatively small, not contiguous. Me-
tasome scarcely more than half the length of the mesosome, terminal segment
rather broad, and rounded at the tip, with only a very slight indication of a
median prominence. Eyes comparatively large, rounded. Superior antennae with
the last joint of the peduncle but little longer than the 2nd. Inferior antenna 1
unusually short and robust, scarcely reaching beyond the 1st segment of mesosome
11 Crustacea.