24 THE V^OYAGE OF H.M.S CHALLENGER. 



and marks ofi' in front the very small space where the carapace forms the immediate 

 body- wall, at the same time dorsally defining the anterior division of the body, — the 

 cephalic part. Immediately below this area, on each side, the insertion of the adductor 

 muscle of the valves is distinctly seen as an assemblage of small lucid spots. 



The division of the body behind the cephalic part is very large, occupying more than 

 the third part of the length of the body. It is at once seen to answer to the compara- 

 tively small part described above in Paranehalia as the trunk, and is, as in that genus, 

 composed of eight well-defined segments, slightly increasing in size posteriorly, and each 

 bearing a pair of branchial limbs. The ventral surface of this division bulges out 

 as it were in its posterior part, so as to project further dowm than the pleou, whereas the 

 contrary is the case in the two other known genera. 



The pleon is considerably shorter than the trunk and rapidly tapers posteriorly. It 

 is composed of the normal number of segments, none of which, however, exhibits any 

 traces of distinct epimera. 



The tail is very small and narrow, cylindrical in form, and about as long as the three 

 posterior segments of the pleon taken together. It is composed, as in the other genera, 

 of four segments about equal in size, the tliree anterior being slightly denticulate at the 

 posterior edge. The last segment is somewhat dilated at the end, and wants the dentiform 

 projections found in the preceding genus on each side of the anal orifice. 



The eyes (figs. 8, 9, 0) exhibit a quite rudimentary condition, wanting, as they do, 

 every trace of pigment and visual elements. They are very small, so as easily to escape 

 attention, and nearly cylindrical in form, or very slightly dilated towards the end, which 

 is obtusely rounded and Cjuite smooth. 



The antennulae (fig. 8, a^) are constructed upon the very same type as in Nehalia 

 and Paranehalia, but appear comparatively shorter and stouter. The first joint of the 

 peduncle is rather massive, irregularly angulated, and, as in the latter genera, very firmly 

 connected with the head. The second joint is scarcely longer than the first, dilated in 

 the proximal part, and rapidly tapering to the end, forming with the succeeding joint a 

 strong geniculate bend. It bears on the inner side near the end a few recurved setas, but 

 is otherwise, like the first, quite smooth. The third joint is scarcely more than half as 

 large as the preceding, constricted at the base and somewhat dilated toward the end, with 

 the terminal edge forming on the outer side an obtuse angle. The fourth joint is still 

 smaller but rather broad, and juts out anteriorly as a slightly curved narrow process, 

 strongly compressed and very finely denticulate at the anterior edge. As in Nehalia 

 and Paranehalia a lamellar appendage is articulated outside at the base of this process. 

 This appendage is, however, rather small and of a somewhat fusiform shape, with a few 

 small spines along the anterior edge, two of which are afiixed to an angular projection 

 about the middle. Of the numerous slender bristles which clothe the corresponding 

 lamella in the two other generaj there is no trace to be detected. The fiagellum seems 



