10 G. O. Sars. 



iug outside a very delicate, anteriorly-curving, sensory bristle. 

 The remaining part of the antennula is of uniform breadth 

 throughout, and is armed on the inner side with a row of 



4 or 5 strong, dark-coloured denticles. The tip is trans- 

 versely truncated, and armed with several small spinules, carry- 

 ing, moreover, in the middle, the usual fascicle of olfactory 

 papillæ, none of which is of any considerable length. With- 

 in the proximal part of each antennula a distinct muscle is 

 seen, issuing from the rostral prominence and passing to the 

 anterior margin of the antennulæ; it is the retractor muscle 

 of these appendages. The protractor muscles, on the other 

 hand, lie wholly within the head, passing from the region of 

 the eye, downwards to the rostral prominence, where they 

 join the bases of the antennulæ. 



The antennæ (see PI I, figs. 1 & 2) are very power- 

 fully developed, constituting, as usual, the chief locomotory 

 organs of the animal. They each consist of a thick and 

 muscular stem, originating with a broad base from the sides 

 of the head, and of 2 slender rami. The proximal part of 

 the stem is bent in an elbow-shaped manner, and is closely 

 annulated transversally, carrying outside, close together, two 

 delicate sensory bristles. The distal part is slightly nar- 

 rowed, and exhibits below, at some distance from the tip, a 

 very conspicuous, anteriorly-curving, dentiform projection. At 

 the tip are attached 2 unequal bristles, the longer of which 

 projects between the insertions of the two rami. Of the 

 latter, the inner, or lower one, is a little longer than the 

 upper, and is 3-articulate, with the 1st joint the largest, and 

 the 2nd somewhat shorter than the 3rd. This ramus carries 



5 setæ, besides a small apical spine. Of the setæ, however, 

 that issuing from the 1st joint is spiniform, sabre-like, and much 

 longer than the others, amounting to about 3/4 of the length 



