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



either side, so as to form, along with the telsou, a complete caudal fan. The outer plate 

 is the larger of the two, and has the outer edge rather arched in the middle, and 

 terminating posteriorly in a short dentiform projection, invariably placed at some 

 distance from the apex. From this projection, too, a distinctly marked transverse suture 

 passes obliquely across the plate, marking off the linguiform terminal portion of the 

 plate as a distinct joint, which, to a certain extent, would even appear to be movable by 

 the help of two thin muscles, proceeding to it from the proximal segment of the plate. 

 Tlie whole of the interior border of this plate, as also the terminal lolje, is fringed with a 

 dense row of ciliated bristles. The inner plate is generally both somewhat shorter and 

 much narrower than the outer, and lanceolate in form, being also fringed around all 

 its borders with a row of similar Ijristles. 



Nervous System. —The ventral chain of ganglia (see PI. VIII. fig. 19) is more 

 especially distinguished by the very inconsiderable degree of centralisation observed in 

 the portion belonging to the anterior division of the body, exhibiting thereby a striking 

 resemblance to that in some lower forms of Crustacea, for example in Isopoda and 

 Amphipoda. The several ganglia are, on the whole, of a very uniform appearance, and 

 connected by rather long double commissures, their original twofold nature being also 

 distinctly perceptible. Exclusive of the cephalic or supra-cesophageal ganglion, nine 

 ganglia are found to belong to the anterior division of the body, and six to the posterior, 

 making in all fifteen difi'erent ganglia. Of these, only the two foremost (1-2), providing 

 the buccal parts with nerves, are partly coalescent, while all the rest are distinctly 

 definable. The commissures connecting the second and third ganglia are certainly very 

 short, leaving between them only a small rounded opening ; but the rest are of con- 

 siderable length and of distinctly fibrous structure. On the u]3per side of each of the 

 ganglia, counting from the fourth to the eighth, is observed a ligature-like, transverse 

 commissure (see fig. 20), arching over and holding in position the great ventral artery 

 (a) which, passing forward, sends off on each side immediately behind the ganglia a 

 lateral branch for the corresponding leg and its several appendages. 



The ganglia of the tail (see fig. 19) are somewhat inferior in size to those of the trunk, 

 and are connected by much longer commissures, which, moreover, are placed close together. 

 The last caudal ganglion (6), occurring at the base of the caudal fan, is somewhat 

 larger than those preceding it, and sends off numerous nerves, some entering the telson, 

 some the uropoda, and finally innervates the muscles surrounding the anal opening. 



Coloiir. — As has been stated hy the late Dr. v. Willcmoes-Suhm, all the specimens 

 examined by him belonging to this genus were, while still alive or in a fresh state, of a 

 vivid red colour, and in reality it is probable that this characteristic is common to all the 

 species, a similar colour being likewise observed in several other deep-sea Crustacea. . 



Habitat. — All tlie species belonging to the present genus seem to Ije well marked 

 deep-sea forms. The least depth from which specimens have been obtained is 



