386 A HISTORY OF EECENT CRUSTACEA 



and fifth joints are, Hansen says, in this species firmly- 

 fused. Of the swimming-feet he observes that the 

 feathered setge are attached a little within the margin, to 

 obtain support when displayed for swimming, and to have 

 a resting-place when folded away between the strokes. 

 Eight new species are named and described by Beddard 

 from the Challenger explorations, all from considerable and 

 some from very great depths. 



Ilyarachna, Sa,rs, 1869, ' mud-spider,' was named in 

 place of the preoccupied MesostSmis, Sars, 1864, meaning 

 ' narrow in the middle.' The body is suboval, but deeply 

 incised behind the fourth segment of the perseou. The 

 second antennaa are long; the mandibles have a molar 

 tubercle, and either have a small three-jointed ' palp' or 

 are without one. The first limbs of the person are not 

 elongate, the second usually more robust than the rest, the 

 third and fourth in general very elongate, the fifth and 

 sixth natatory, with an unguiform seventh joint, the 

 seventh long and slender, with the joints scarcely flattened, 

 the nail long and curved. The uropods are simple, lying 

 close to the pleon. Sars has described five Norwegian 

 species, of which the first was Ili/arachna lovgicornis. 

 Ilyarachna quad/rispinosa, Beddard, was brought by the 

 challenger from Kerguelen. 



Besmosoma, Sars, 1864, ' a chain-like body,' has the 

 segments marked off by constrictions which are commonly 

 deep ; the three hinder segments of the pleon are larger 

 than those which precede. The second antennee are shorter 

 than the body, slender in the female, robust in the male. 

 The mandibles have a dentate cutting-edge, spine-row, 

 molar, and usually a three-jointed ' palp,' ending in a long 

 unguiform spine. The first four pairs of limbs are short 

 and robust, the last three natatory, but with the fifth and 

 sixth joints not greatly expanded, edged with spines that 

 are flattened but not plumose ; the seventh joint is narrow 

 and stiliform. The uropods are simple, two-jointed, the 

 last joint being the larger. Sars has described four Nor- 

 wegian species, Besmosoma lineare, armaium, aculeatum, and 

 tenuimdnum, of which aculeatum has no mandibular ' palp.' 



