download pdf

97
From the nearly-allied genus Mane .iselliis Harger it is prominently distinguished,
among other things, by the presence of well-developed mandibular palps. Five
species of this genus have been recorded, only one of which belongs
fauna of Norway.
Asellus aquaticus (Lin.).
(PL XXXIX.)
(htiscus aquaticiis, Linne, Fauna Svecia, ed. 2da, p. 500.
S}-n : Sqnilla aselhts, de Geer.
Oymothoa aquatica, Fabr.
Asellus vulgaris, Latr.
IdotJiea aquatica, Latr.
to the
Specific Characters. Body oblong oval, in male slightly widening behind,
in female with the greatest width about in the middle, and equalling half the
length, not including the caudal segment. Cephalon broader than it is long, with
a slight setotis prominence on each side near the base, frontal edge straight.
Segments of mesosome of nearly uniform size, lateral parts transversely truncated
at the tip, and clothed with stiff hairs. Caudal segment about half the length of
the mesosome, rounded quadrangular in form, and fringed all round with stiff
hairs; terminal edge bisinuate. with an obtuse median prominence. Eyes consist-
ing each of only 4 visual elements, ocular pigment not confluent. Superior antennae
about the length of the peduncle of the inferior ones, flagellum composed of
10 12 articulations. Inferior antennas not quite as long as the body, flagellum
more than twice the length of the peduncle. Legs densely clothed with spiniform
bristles; 1st pair rather short, with the propodos in female oblong oval,
in male
subtriangular, inner edge forming an obtuse prominence, armed with 3 strong
spines. Uropoda with the rami more than twice as long as the basal part, and
edged with scattered spiniform bristles. Colour very dark, fuscous, spotted with
white. Length of adult female 8 mm.,
of male 12 mm.
Remarks. This form has been treated of in detail by the present author
in one of his earlier works: "Crustaces d'eau douce de Norvege", to which the
reader may lie referred for detailed information on the more minute anatomy
and the development.
Occurrence. The species would seem to occur everywhere in Norway,
especially in small ponds that have a muddy botfflm,
and are covered at the sur-
face with Lemna. It is also occasionally met with in slow streams, and in larger
lakes, but never at any considerable depth.
present author).
Distribution. The European continent everywhere, Siberia, Algieria (the
13 Crustacea.