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rather peculiar, and somewhat recalls the species of the genus Ischnosoma, but
in the anatomical details it approaches more nearly to the genus Desmosoma.
The coarse armature of the body will serve for at once distinguishing it from the
species of either of the 2 above-mentioned genera.
Occurrence. This species was first observed in the inner part of the
Christiania Fjord, at a depth of 15 20 fathoms. Subsequently
I have found it,
also in several other localities of the Norwegian coast, as far north as the Lofoten
Islands, but it seems everywhere to be very rare. Out of Norway, it has not yet
been recorded.
Fam. 5. Munnopsidse.
Characters. Body, as a rule, shorter and more compact than in the
Desmosoniidce, with the 2 divisions of mesosome very sharply defined. Eyes ab-
sent. Superior antenna? with the basal joint remarkably large and broad, flagel-
lum generally well developed. Inferior antenna? very much elongated, and of
same structure in the two sexes. Oral parts on the whole normal, though the
structure of the mandibles is rather different in the different genera. 1st pair
of legs generally smaller than the others, but never subcheliform;
ing ones, as a rule, very much elongated and ambulatory
the 3 succeed-
in character. The 3
posterior pairs of legs very unlike the preceding ones, and pronouncedly natatory,
the outer joints being lamellarly expanded, and fringed with densely plumose setae.
Uropoda small, simple
or biramous.
Remarks. In the restriction here adopted, this family is prominently
distinguished by the peculiar structure of the 3 posterior pairs of legs, which
constitute very powerful natatory organs, by which the animal is enabled to move
very rapidly through the water in a backward direction. This motion has not,
as in certain DesmosomidoB, the character of an even run, hut is effected by
sudden jerks, and is, on the whole, much more energetic, a fact easily accounted
for by the rather different structure of the natatory legs, and the densely plumose
setae with which the very much expanded outer joints are fringed. The
family comprises at yet 7 genera, 6 of which are represented
in the fauna of
Norway, and will be treated of below, the 7th genus, Acanthocope, having been
established by Mr. F. Bcddard, to include -2 species from the Challenger Expedition.