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 sjjines 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 row of flattened 

 spines successively increasing in length distally, 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 

 female 3y 3 mm., of male 2 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 the 3 posterior segments of the mesosome, as also by the structure of the 1st 

 pair of legs, and the shape of the caudal segment. 



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. 



(PI. IilV, fig. 2.) 



Desmosoma armatmrt, G. O. Sars, Om en anomal Gruppe af Isopoder. Chr. 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 



