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143
Pseudarachna hirsuta,
(PI. LXIII.)
G. 0. Sars.
Ilyaraclma Idrsuta, G. 0. Sars, Om en anomal Gruppe af Isopoder. Chr. Vid. Selsk. Forhamll.
1863, p. 9.
Specific Characters. Body more than twice as long as it is broad, with
the greatest width across the 2nd segment of mesosome, surface everywhere clothed
with stiff bristles. Cephalon very broad and highly convex above, front obtusely
rounded, lateral parts obliquely expanded. Each of the 4 anterior segments of
mesosome armed dorsally with 2 juxtaposed denticles, and laterally with an up-
turned spine. The 3 posterior segments of mesosome combined scarcely exceeding
half the length of the anterior division, the anterior segment the largest, and but
slightly emarginated behind ; last segment rather small. Caudal segment some-
what longer than it is broad at the base, tip obtusely pointed. Superior antennas
with the basal joint produced outside to a linguiform lamellar expansion carrying
at the tip 2 auditory seta?; flagellum scarcely longer than the 2nd peduncular joint,
and composed of only 3 articulations. Inferior antenna? about one and a half times
as long as the body, the 2 outer joints of the peduncle rather strongly built, and clothed
with scattered spiniform bristles, flagellum very slender and composed of 14 narrow
and elongated articulations. 1st pair of legs extremely slender, with the propodos
long and narrow; 2nd pair very robust, with the ischial joint much expanded
distally, and clothed inside with strong seta?.. The 2 succeeding pairs shorter and
much narrower than the 2nd pair, with the dactylar joint not unguiform, tipped
with diverging bristles. 1st pair of natatory legs considerably larger than the other
2, though having the outer joints but slightly expanded and fringed with a very
restricted number of ciliated seta?; last pair extremely slender, with the propodal
joint very narrow, linear. Uropoda with the basal joint rather large, oblong oval,
and edged with numerous short plumose seta?, terminal joint extremely minute,
nodiform. Colour whitish grey. Length of adult female 2 1
/-2
mm.
Remarks. This form was described by the present author as early as in
the year 1863, and at that time referred to the genus Ilyarachna. It is easily
recognizable by the densely hirsute body and the peculiar structure of the legs.
More frequently, however, it is so closely obtected with muddy particles adhering
to the stiff bristles, that its true form is rather difficult to observe.
Occurrence. The only place where I have hitherto met with this peculiar
form, is in the innermost part of the Christiania Fjord, where a few specimens
were taken from a depth of about 30 fathoms, muddy bottom. Out of Norway,
it has not yet been recorded.