510 THE VOYAGE OF H.M.S. CHALLENGED. 



from these coarse granulations are immediately behind the eyes, the fronto-lateral margin, 

 the dorsal surface of the rostrum, and the median line. 



The somites of the pleon are also coarsely granulated, but the granulations do not run 

 longitudinally except along the median ridge, where every somite has an anterior and a 

 posterior cusped elevation on the exposed portion, more or less prominent continuously 

 to the telson. All the somites exhibit three divisions, an anterior, a median, and a 

 posterior. The anterior is perfectly smooth, and when the animal is extended, as in 

 swimming, it is always covered by the posterior margin of the preceding somite. In the 

 first somite the anterior division passes under the carapace, and a fringe of hair along the 

 anterior margin of the central division assists in closing up the line of junction between 

 it and the carapace. The median division is separated from the posterior by a line of 

 depression, which is again divided into three parts, a central and two lateral, each of 

 which is furnished with a strong pointed cusp or tooth. The central cusp is pointed 

 directly forwards, the lateral obliquely outwards. The coxal plate is produced as deeply 

 as the carapace, which is covered by the anterior margin of the coxal plate, while the 

 posterior is overridden by the next succeeding somite. The postero-inferior angle is 

 rounded off and the anterior is produced to a sharp point. The second somite is longer 

 than the first, and the coxal plate is wider and slightly deeper, and has the margin 

 produced into three sharp teeth, one at the anterior angle, one, the largest, central, and 

 one at the posterior angle. The third somite resembles the second in all but the presence 

 of a tooth at the anteroinferior angle. The fourth somite has the dorsal surface of the 

 posterior division produced posteriorly to an obtuse angle, and the coxal plates resemble 

 those of the third. The fifth differs from the fourth in being narrower, in having the 

 posterior cusps on the median line flanked at the base by two oblique ones, and in having 

 the coxal plate directed inferiorly backwards, the tooth at the posterior angle being the 

 largest. The sixth somite has the coxal plate reduced to a single tooth-like process, 

 between which and the posterior margin the posterior pair of pleopoda articulates. 



The telson, besides the central cusp on the anterior portion, has a couple of continuous 

 ridges running longitudinally, well defined, and converging to the extremity of the telson, 

 giving to this somite a fluted appearance. 



The three. anterior somites of the pleon articulate laterally with those posterior to 

 them by a small prominence on the posterior margin, fitting into a hollow in the 

 anterior margin of the succeeding somite, and the posterior three and telson by a process 

 on the anterior margin being enclosed within a space which is formed by a flat process 

 projecting backwards and upwards, and pressing laterally against the somite posterior to it. 



The ophthalmopoda are supported on a free ophthalmic somite implanted immediately 

 beneath the rostrum. The peduncle is extremely small and short, while the ophthalmus 

 is very large and conspicuous, being almost globular, and occupying nearly the entire 

 space between the rostrum and the orbital tooth. 



