79 



32. Isias clavipes, Boeck. 



(PI. LIII, LIV). 



Isias cJari/ii's. I'xicck. Oversigt over de veil Norges Kyster iagttagne 



Chr. Vid. Selsk. Forli. 1864, p. 242. 



: Isias Bonnieri, Canu. 



Specific Characters. Female. Anterior division of body, seen dorsally, 

 regularly elliptical in outline, greatest width about equalling half the length, and 

 occurring in the middle, anterior extremity narrowly rounded, posterior somewhat 

 blunted ; seen laterally, considerably vaulted above. Lateral parts of last segment 

 of metasome rounded off. Urosome exceeding half the length of the anterior 

 division, and slightly asymmetrical, genital segment somewhat tortuous, with a 

 rounded protuberance to the left side of the dorsal face, and carrying below 2 

 somewhat unequal spiniform, recurved processes, one on each side of the genital 

 area. Caudal rami sublinear in form, being nearly 4 times as long as they are 

 'broad, apical setse not much elongated. Anterior antennae, when reflexed, scarcely 

 reaching beyond the anterior division, some of the anterior bristles on the proximal 

 part spiniform. Last pair of legs with a strong spine on the hind face of the 

 2nd basal joint issuing near the outer corner, inner ramus very small, with 3 

 or 4 natatory setas; unguiform projection of outer ramus somewhat curved and 

 distinctly denticulated. 



Male more slender than female, with the urosome longer and narrower, 

 middle segment produced on right side to a very conspicuous conical projection 

 pointing straight outwards. Right anterior antenna with the middle section mode- 

 rately tumefied. Last pair of legs with the inner ramus on right side obsolete, 

 on left transformed to a somewhat irregularly folded lamella without any setae; 

 distal joint of outer rami with 4 marginal spines, that of right leg much the 

 larger and of oval quadrangular form, with an irregular protuberance at the base 

 inside, and with the outermost spine very strong; that of left leg with the inner 

 edge finely ciliated and angularly produced both at the base and at the end. 



Colour. Body, as a rule, semipellucid and of whitish colour, sometimes, 

 however, in female exhibiting a light bluish hue. 



Length of adult female reaching 1.35 mm., of male about the same. 



Remarks. As observed above, this is the only species of the genus as 

 yet known, the form described by Mr. E. Canu as Isias Bonnieri being unquestio- 

 nably identical with Boeck's species. It may be easily recognized by the general 

 form of the body, the comparatively short anterior antennse, and the peculiar 

 structure of the last pair of legs., especially in the male. 



