123 



bulatory, and very much elongated, terminating in a slender claw. Uropoda of 

 moderate length, simple, Inarticulate. 



Remarks. — This is a very distinct genus, exhibiting in some characters 

 an approach to the genus Deamosoma, though being well distinguished, among 

 other things, by the non-natatory character of the posterior pairs of legs, and by 

 the peculiar appearance of the 4th and 5th segments of the mesosome. The genus 

 comprises as yet 5 species, 3 of which (I. spinosum, bacillus and bacilloides) have 

 been described by Mr. Fr. Beddard from the Challenger Expedition, the other 2 

 being northern forms. Of these the one (Z quadrispinosum, G. 0. Sars) was 

 procured during the Norwegian North Atlantic Expedition, the other belongs to 

 the fauna of Norway, and will be described below. 



Isehnosoma bispinosum, G. 0. Sars. 



(PI. LII.) 



Isehnosoma bispinosum, G. 0. Savs, Beretning om en i Sommeren 1865 foretagen zool. JReise 

 ved Kysterne af Christiamas og Chvistiansands Stifter, p. 34. 



Specific Characters. — Body sublinear in form, more than 5 times as long 

 as it is broad, the greatest width occurring far in front. Cephalon sub-quadrang- 

 ular in outline, very slightly notched on each side for the insertion of the 

 antenna?, frontal part obtusely truncated. 1st segment of mesosome deeply 

 emarginated in front, lateral parts produced to obliquely anteriorly pointing 

 spiniform projections more prominent in male than in female. Middle section, 

 comprising the firmly connected 4th and 5th segments of mesosome, about half 

 the length of the body, and pronouncedly hourglass-shaped, being in male ex- 

 tremely narrow in the middle. The last 2 segments of mesosome very short. 

 Caudal segment oval in form, gradually widening somewhat distally, tip evenly 

 rounded. Superior antennae reaching beyond the middle of the penultimate pe- 

 duncular joint of the inferior ones, 1st joint very short, 2nd long and slender, 

 with 3 remarkably strong sets inside, 3rd half the length of the former, flagellum 

 3-articulate. Inferior antennae fully as long as the body, the outer 2 joints of 

 the peduncle long and slender, edged with scattered bristles, flagellum about the 

 length of the peduncle, and composed of numerous (about 20) articulations. 1st 

 pair of legs much shorter than the others, and pronouncedly prehensile, carpus 

 greatly expanded, exhibiting a well-defined palm armed with several short den- 

 ticles, and, at the lower corner, a slender spine. The remaining legs of exactly 

 the same structure and very slender, terminating in a long and narrow claw. 

 Copulative appendages of male rather broad, with the digitiform process quite 



