1098 



CRUSTACEA. 



or two setse at apex ; and the palpus articulated with it is a single 

 oblong joint, bearing a very long naked seta, many times longer than 

 the joint. 



The maxillipeds, which are longer than the anterior feet, have a 

 long basal joint, which stands at right angles to the body; the organ 

 is then flexed forward, and the remaining part is three-jointed, and 

 together about as long as the basal joint. Each of the joints bears a 

 few stout and long setulous setse, which, in the natural position of the 

 parts, reach forward to the mouth. At the inner apex of the basal 

 joint there are two or three of these setulous setse on a common base, 

 and above, there are a few other setse, which are naked. 



The anterior feet are either straight, or flexed like the maxillipeds. 

 They are three-jointed and bear a few short spinulous setse (see Plate 

 76). The first or basal joint is longer than the third, and has in one 

 species a naked spine on the inner margin near the middle, and an- 

 other on the outer towards the apex. 



The natatories have the usual form, except that in two species out 

 of the three collected, there is a long seta extending outward from the 

 second of the two basal joints, which is seen in an upper view pro- 

 jecting from the side of the body when the animal is swimming. 

 There are thus four setse either side (as there are four natatories), and 

 in one species they were delicately coloured plumes. We did not suc- 

 ceed in ascertaining whether these plumes or setse are peculiar to one 

 sex alone, or belong to both ; but are inclined to the former opinion. 



The abdomen consists of four or five segments in the species observed. 

 The basal bears one or two setse on either side : it is not always dis- 

 tinct from the following. 



The caudal stylets are styliform and divergent. The setse are very 

 unequal. One is much longer than the others, exceeding the length 

 of the abdomen; the rest are short. 



The cephalo thorax in the species observed is only four-jointed, and 

 is obtuse in front and behind. 



The Oithonse are best distinguished by the antennae, the abdomen 

 and its basal and caudal setse, the lateral setae of the natatory legs. 

 They are very widely distributed in different oceans, yet pertain to 

 few species. 



Oithona, Baird, Zoologist, 1843. 



Scribetta, Dana, Amer. Jour. Sci. [2], i. 227, and Proc. Amer. Acad., 1849, ii. 19; 

 where the following new species are briefly described by the author. 



