91 



more richly setiferous, 3rd joint rather narrow and somewhat exceeding in length 

 the 2nd. First pair of legs with the inner ramus fully twice as long as the outer, 

 2nd joint comparatively slender, apical claws of about the same structure as in the 

 2 preceding species. Natatory legs with the rami more slender than in I. fur- 

 cata, the 3rd joint of the outer ramus in 4th pair being especially of a very nar- 

 row form. Last pair of legs with the inner expansion of the proximal joint nar- 

 rowly rounded and having all 3 marginal setae well developed, distal joint exceed- 

 ingly slender and elongated, narrow linear in form, and having one of the lateral 

 seta3 at some distance from the others. 



Body of a whitish colour, faintly tinged with light red. 



Length of adult female about 1 mm. 



Remarks. I think I am right in considering the above-described form to 

 be identical with that recorded by Seb. Fischer as Thisbe ensifera. In size and 

 external appearance it is very like 1. furcata, and was also adduced to that 

 species by Prof. Brady. On a closer examination, however, it is found to differ 

 in the more elongated and more richly setiferous anterior, antennae, and especi- 

 ally in the exceedingly slender form of the distal joint of the last pair of legs. 

 In the structure of the other legs also, and in the relative length of the caudal 

 setae, well-marked differences from 1. furcata are found to exist. 



Occurrence. This form is by no means unfrequent off the Norwegian 

 coast. In the upper part of the Christiania Fjord, for instance, it occurs rather 

 plentifully in depths ranging from 6 to 20 fathoms; and I have also met with it 

 in several localities on the west coast, and even in Finmark. 



Distribution. Madeira (Fischer). 



55. Idya tenera, G. 0. Sars, n. sp. 



(PL LIH, fig. 2). 



Specific Characters. Female. Form of body very slender, with the an- 

 terior division, seen dorsally, oblong fusiform in outline, and the epimeral plates 

 separated by deep lateral incisions. Urosome about half the length of the anterior 

 division, and gradually tapering distally. Caudal rami very short, apical setae 

 somewhat less elongated than in I. ensifera. Anterior antennae moderately slender, 

 with the 3rd joint fully as long as the 2nd. First pair of legs with the inner 

 ramus comparatively shorter than in 7. ensifera and more resembling that in 7. 

 furcata, 2nd joint, however, scarcely longer than the 1st. Last pair of legs with 



