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antenna? originating close together from the front, hasal joint large, sub-quadran-
gular in form, inner corner somewhat more projecting than the outer, flagellum
not much elongated. Inferior antennae exceeding the body in length. Mandibles
very massive, with an oblique crest outside, cutting edge undivided, molar ex-
pansion narrow, tipped with scattered spines, palp distinct, though
rather feeble.
Maxillipeds with the 2nd joint of the palp very large and expanded, antepenulti-
mate joint rounded at the inner corner, penultimate joint very slightly produced
at the end inside, epignath exceedingly large. 1st pair of legs comparatively small,
simple; 2nd pair considerably larger and densely edged with spines, dactylus long
and slender. The 2 succeeding pairs of legs slender and elongated,
with the
ischial joint considerably exceeding in length both the preceding and succeeding
joints, carpal and prop'odal joints slender, linear, and each having at the end out-
side, a very fully developed auditory seta, dactylus long and slender. The 2
anterior pairs of natatory legs of similar structure, with the carpal joint exceed-
ingly large and expanded, cordiform in outline, propodal joint much narrower,
oblong, dactylus well developed; last pair much narrower than the 2 preceding
pairs, with the carpal joint but slightly expanded, propodal joint linear, dactylus
much elongated. Female operculum narrow, carinated along the middle, and densely
setous at the edges; male operculum transformed in the usual manner. Uropoda
comparatively small, Inarticulate, proximal joint lanielliform and edged
ated setae, distal joint very small.
with cili-
Remarks. This genus was established by the present author as early as
in the year 1863; but the generic name Mesostenus proposed at that time being
already appropriated, it was subsequently changed to Ilyarachna. The genus is easily
distinguishable from that of Muitnopsis, both as regards its outward appearance,
and the structure of the several appendages. On a closer anatomical examination
of the several species previously referred to this genus, I have found it necessary
to separate some of them as types of distinct, though nearly-allied genera. In
the restriction here adopted, it comprises 3 Norwegian species, to be described
below. Moreover, 2 exotic species have been recorded as belonging to this genus,
viz., I. quadrispmosa Beddard from the Challenger Expedition, and /. polita
Bonnier from the Gulf of Gascogne. Of these, the last-named is unquestionably
a true Ilyarachna, whereas the Challenger species seems to differ rather markedly,
and should therefore more properly be regarded as the type of a separate genus.