download pdf

126
form, with the proximal joints rather incrassated. 1st pair of legs moderately
strong, slightly attenuated, carpus not dilated, and only clothed inside with
scattered bristles, propodos narrow, suhlinear. The 3 succeeding pairs very densely
clothed with spines arranged on the outer Joints in a double row, dactylus com-
paratively small. The 3 posterior pairs of legs successively somewhat diminishing
in size, basal joint large and muscular, meral joint very small, triangular, carpal
joint large, oblong, compressed and edged inside with a regular
spines successively increasing in length dis tally,
row of flattened
and more numerous in male than
in female, propodal joint oblong lamelliform, and likewise, fringed with slender
spines, dactylus slender, styliform, with 3 sub-apical bristles. Uropoda somewhat
exceeding half the length of the caudal segment, distal joint sublinear, 4 times
as long as the proximal one. Colour whitish, semi-pellucid. Length of adult
of male 2 mm.
female 3 l
/% mm.,
Remarks. The present species may be regarded as the type of the genus,
and is easily distinguished from the succeeding one by the fuller development
of tiie 3 posterior segments of the mesosome, as also by
pair of legs, and the shape of the caudal segment.
the structure of the 1st
Occurrence. The species occurs along the whole south and west coasts of
Norway, from the Christiania Fjord at least to the Lofoten Islands,
and is found
in depths ranging from 30 to 100 fathoms. The animal being extremely fragile,
only imperfect specimens are generally procured by the aid of the ordinary dredge.
To catch it in an uninjured state, very delicate dredging implements are required,
and it is indeed by such means that I have succeeded in getting many Crustacean
forms, which otherwise would have escaped my attention. The swimming motion
of the animal has the character of a quite even run through the water in a back-
ward direction. During this run, the 3 posterior pairs of legs
are seen to be
in a rapid vibrating motion, whereas the anterior pairs are extended in front.
At other times the animal is seen creeping slowly along the bottom in the or-
dinary manner. Out of Norway, this form has not yet been recorded.
2. Desmosoma armatum, G. 0. Sars.
(I'l. LIV, fig. 2.)
Desmosoma armatum, U. 0. Sars, Om en anoiiial Gruppe af Isopoder. Clir. Vid. Selsk. Forhl.
1863, p. 12.
Specific Characters. Body comparatively less slender than in the preced-
ing species, with the posterior division considerably narrower than the anterior