135 



antennae originating close together from the front, basal joint large, sub-quadran- 

 gular in form, inner corner somewhat more projecting than the outer, flagellum 

 not much elongated. Inferior antenna? exceeding the body in length. Mandibles 

 very massive, with an oblique crest outside, cutting edge undivided, molar ex- 

 pansion narrow, tipped with scattered spines, palp distinct, though rather feeble. 

 Maxillipeds with the 2nd joint of the palp very large and expanded, antepenulti- 

 mate joint rounded at the inner corner, penultimate joint very slightly produced 

 at the end inside, epignath exceedingly large. 1st pair of legs comparatively small, 

 simple ; 2nd pair considerably larger and densely edged with spines, dactylus long 

 and slender. The 2 succeeding pairs of legs slender and elongated, with the 

 ischial joint considerably exceeding in length both the preceding and succeeding 

 joints, carpal and propodal joints slender, linear, and each having at the end out- 

 side, a very fully developed auditory seta, dactylus long and slender. The 2 

 anterior pairs of natatory legs of similar structure, with the carpal joint exceed- 

 ingly large and expanded, eordiform in outline, propodal joint much narrower, 

 oblong, dactylus well developed; last pair much narrower than the 2 preceding 

 pairs, with the carpal joint but slightly expanded, propodal joint linear, dactylus 

 much elongated. Female operculum narrow, carinated along the middle, and densely 

 setous at the edges; male operculum transformed in the usual manner. Uropoda 

 comparatively small, biarticulate, proximal joint lamelliform and edged with cili- 

 ated setas, distal joint very small. 



Remarks. — This genus was established by the present author as early as 

 in the year 1863; but the generic name Mesostenus proposed at that time being 

 already appropriated, it was subsequently changed to Ilyarachna. The genus is easily 

 distinguishable from that of Munnopsis, both as regards its outward appearance, 

 and the structure of the several appendages. On a closer anatomical examination 

 of the several species previously referred to this genus, I have found it necessary 

 to separate some of them as types of distinct, though nearly-allied genera. In 

 the restriction here adopted, it comprises 3 Norwegian species, to be described 

 below. Moreover. 2 exotic species have been recorded as belonging to this genus, 

 viz., I. quadrispinosa Beddard from the Challenger Expedition, and I. polita 

 Bonnier from the Gulf of Gascogne. Of these, the last-named is unquestionably 

 a true Ilyarachna, whereas the Challenger species seems to differ rather markedly, 

 and should therefore more properly be regarded as the type of a separate genus. 



