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bulatory, and very much elongated, terminating in a slender claw. Uropoda of
moderate length, simple, Inarticulate.
Remarks. This is a very distinct genus, exhibiting in some characters
an approach to the genus Desmosoma, though being well distinguished, among
other things, by the non-natatory character of the posterior pairs of legs, and by
the peculiar appearance of the 4th and 5th segments of the mesosome. The genus
comprises as yet 5 species, 3 of which (I. spinosum, bacillus and bacilloides) have
been described by Mr. Fr. Beddard from the Challenger Expedition, the other 2
being northern forms. Of these the one (I. quadrispinosum, Gr. 0. Sars) was
procured during the Norwegian North Atlantic Expedition, the other belongs to
the fauna of Norway, and will be described below.
Ischnosoma bispinosum, CI. 0. Sars.
(PI. LII.)
Ischnosoma bispinosum, G. 0. Sars, Beretning om en i Sommeren 1865 foretayen zool. Reise
ved Kysterne af Ghristianias og Christiansands Stifter. p. )54.
Specific Characters. Body sublinear in form, more than 5 times as long-
as it is broad, the greatest width occurring far in front. Cephalon sub-quadrang-
ular in outline, very slightly notched on each side for the insertion of the
antennae, frontal part obtusely truncated. 1st segment of mesosome deeply
emarginated in front, lateral parts produced to obliquely anteriorly pointing
spiniform projections more prominent
in male than in female. Middle section.
comprising the firmly connected 4th and 5th segments of mesosome,
about half
the length of the body, and pronouncedly hourglass-shaped, being in male ex-
tremely narrow in the middle. The last 2 segments of mesosome very short.
Caudal segment oval in form, gradually widening somewhat distally, tip evenly
rounded. Superior antennae reaching beyond the middle of the penultimate pe-
duncular joint of the inferior ones, 1st joint very short, 2nd long and slender,
with 3 remarkably strong seta? inside, 3rd half the length of the former, fiagellum
3-articulate. Inferior antennae fully as long as the body, the outer 2 joints of
the peduncle long and slender, edged with scattered bristles, Hagellum about the
length of the peduncle, and composed of numerous (about 20)
articulations. 1st
pair of legs much shorter than the others, and pronouncedly prehensile, carpus
greatly expanded, exhibiting a well-defined palm armed with several short den-
ticles, and, at the lower corner, a slender spine. The remaining legs of exactly
the same structure and very slender, terminating in a long and narrow claw.
Copulative appendages of male rather broad, with the digitiform process quite