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Tribe 3.
VALVIFERA.
Remarks. The chief character by which this group is defined from all
other known Isopoda, consists in the peculiar structure of the uropoda, which,
like a pair of folding doors, arch over the lower face of the metasome,
thus form-
ing a shelter for the delicate pleopoda, the latter being for the most part branchial
in character, though the anterior pairs may at times also serve as swimming limbs
for propelling the animal through the water. We only know of 3 families belong-
ing to this tribe, viz., the Idotheidce, Arctitridce and Cludiludw, the last of which,
however, is still very imperfectly known. The first 2 families are represented in
the fauna of Norway, and will be treated of below.
Fam. 1. Idotheidae.
Characters. Body more or less depressed, with the segments of mesosome of
uniform appearance, coxal plates sometimes distinctly defined, sometimes confluent
with the segments. Metasome with some, or all of the segments consolidated to
form a large terminal piece, carrying the normal number of pleopoda. Superior
jintennse comparatively small, with the flagellum mii-articulate. Inferior antennae
more or less elongated, and originating outside the superior, from the lateral corners
of the cephalon. Oral parts on the whole normal, though
the mandibles are al-
ways without palps,^and the joints of the maxillipeds are often reduced in number.
Legs rather strongly built, increasing in length posteriorly, the 3 anterior pairs