14 THE VOYAGE OF H.M.S. CHALLENGER. 



considerably more elongate, though scarcely exceeding half the length of the peduncle. 

 It slightly tapers towards the end, and is composed of five articulations, the first of 

 which is nearly twice as long as the four others combined. All the articulations are 

 densely beset with bristles, especially along the anterior edge, where the bristles are 

 arranged in distinctly defined fascicles increasing in length toward the apex. On closer 

 examination, some of the setae are found to be densely ciliated along one of their edges, 

 and besides there is found in each fascicle an exceedingly delicate and pellucid ribbon- 

 shaped appendage (fig. 5), answering to the so-called olfactory cilia in other Crustacea. 

 According to the statements of the late Dr. v. Willemoes Suhm, the flagellum in the adult 

 male has a very different appearance from that in the female, being greatly expanded, and 

 without any distinct articulations. In the male of Nebalia, the flagellum is also some- 

 what different from that in the female, but the difference here consists chiefly in this part 

 being more elongate and having dense clusters of sensory bristles on the proximal joints. 

 The antennae (fig. 1, a 2 ; fig. 7) are somewhat more elongate and slender than the 

 antennulae, and affixed in close approximation to the latter, so as partly to cover them at 

 the base. They are composed of an elongate, triarticulate peduncle, geniculate at the 

 middle, and a single multiarticulate flagellum. The first joint of the peduncle is short 

 and thick, somewhat similar to that of the antennulae and without spines or bristles. 

 The second joint is also quite smooth, but considerably more elongate, cylindrical in 

 shape, and, like the antennuke, forming a more or less distinct, elbow-shaped bend with 

 the basal joint. The last joint of the peduncle is still more elongate and close to its base 

 abruptly curved, so as to render the peduncle distinctly geniculate at the middle. The 

 anterior edge of this joint is somewhat irregularly flexuous, forming above, at the curvature 

 of the joint, a rounded, knee-shaped protuberance, beset with short bristles ; two similar 

 but less prominent setose protuberances follow further below, and, besides, two somewhat 

 recurved dentiform projections are found at the same edge, the one nearly in the middle, 

 the other at the end. The outer part of the anterior edge is, moreover, beset with slender 

 ciliated setae, rapidly increasing in length towards the end, and continued transversely 

 on the inside of the joint, so as partly to project also on the posterior side ; these setae 

 are very elongate, almost reaching to the end of the flagellum. The posterior edge of 

 the joint has only a single seta at the middle, but this seta is very strong and more 

 densely ciliated than the others. The flagellum is considerably shorter than the peduncle, 

 cylindrical in form, and composed of six distinctly defined joints, the first of which is by 

 far the longest, and about equals the three succeeding in length. At the end of each of 

 the joints anteriorly, a dense fascicle of bristles occurs, and in addition the first joint has 

 three similar fascicles along its anterior edge. According to the statements of the late 

 Dr. v. Willemoes Suhm, the antennae in the adult male do not differ materially from 

 those in the female, whereas in the male of Nabalia the flagellum is extremely elongate, 

 slender and filiform. 



