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being sometimes pronouncedly subcheliform in structure. The anterior pairs of
pleopoda with the rami densely setiferous, 2nd pair in male with the usual stylet.
Uropoda very large, lamellar, valve-like, closing
over the lower face of the meta-
some; outer part cut off by a transverse suture, and forming a separate plate, in-
side which sometimes occurs another much smaller plate. Incubatory pouch normal.
Remarks. This family is chiefly distinguished from the Arcturida> by the
more or less broad, depressed body, the rather uniform segmentation of the mcso-
some, and the structure of the legs. Some of the largest known Isopoda are in-
cluded in this family. Thus the huge Gtyptonotus antarcticus measures no less
than 3 inches and a half in length, and some of the arctic species of the genus
Chiridothea are scarcely smaller. The family comprises about 10 genera, only
one of which is represented in the fauna of Norway.
Gen. IdOthea, Fabr., 1798.
Generic Characters. Body oval or oblong, distinctly depressed,
with the
coxal plates, beyond the 1 st segment of mesosome, well defined, laminar. Cephalon
subquadrate, with the lateral parts not expanded. Metasome with 3 short seg-
ments exposed in front of the terminal one, the 3rd segment being, however, less
perfectly defined dorsally. Eyes distinct, lateral. Superior
antenme with the
flagellum short, clavate; inferior antenme with the flagellum more or less elongated
and multiarticulate. Mandibles very strong, with the cutting edge divided into 2
superposed dentated lamellae, molar expansion large and thick. Both pairs of
maxilla? of quite normal structure. Maxillipeds with the palp 4-articulate, last
joint lamellarly expanded, masticatory lobe well developed, epignath oblong oval,
turned in front. Legs of rather uniform structure, ambulatory, and as a rule
more strongly built in male than in female, sometimes approaching to a subcheli-
forni character, dactylus in all pairs strong, unguiform, unequally bidentate at the
tip. Uropoda terminating in a single flattened joint, and having
at the base
of this joint, outside, a strong ciliated seta. Male, as a rule, much larger
than female.
Remarks. This is the genus first established, and it accordingly may be
regarded as the type of the family. Numerous species have been described by
different authors from different parts of the Oceans, bat some of these ought
certainly to be separated generic-ally, and even in the restriction adopted by Mr.