REPORT ON THE CRUSTACEA MACRURA. 187 



is distinctly defined and distinguishable from it. It is advanced over the postero- 

 lateral angle of the corresponding plate of the first somite, where it is elevated into 

 a tuberculose enlargement, from whence the margin slightly advances anteriorly, and 

 then gradually and smoothly rounds to the postero-inferior angle, which terminates 

 in a sharp, projecting, posteriorly oblique point. The plate has a central depression 

 corresponding in form to that of the outer margin. 



The third, fourth, and fifth somites resemble the second, being but slightly modified 

 to correspond to the varying curvature of the animal in flexion. The dorsal sulcus 

 of the posterior division gradually decreases in importance, and in each the anterior 

 margin of the coxal plates, instead of overlapping the posterior margin of the preceding 

 as in the second, underlies it. The coxal plates, moreover, become successively narrower 

 and shorter, and all are fringed on the internal surface of the margin with long, plumose 

 hairs directed inwards. 



The sixth somite (PI. XXV. fig. 3) is modified more than any of the preceding, to 

 support its appendages as a portion of the rhipidura. The dorsal sulcus has entirely 

 disappeared, and the posterior margin is centrally elevated into a minute carina, ter- 

 minating in a tooth, and the lateral ridge that defines the separation between the true 

 somite and the coxal plate is armed near the centre with a sharp posteriorly-directed 

 tooth. The coxal plate has an anterior and a posterior angle ; the former is obtusely 

 pointed and directed downwards, the latter acute and posteriorly directed, and the space 

 between the two is concave to receive the basal joint of the posterior pleopod when folded. 



The large and reniform eyes are supported on a small and short peduncle that 

 originates beneath the rostrum, and therefore in close contiguity to the corresponding 

 appendage on the opposite side. The organ rests in a cavity formed by the orbital 

 notch in the anterior margin of the carapace, by a slight hollow on the inferior side of 

 the rostrum, and by a deep depression formed on the upper surface of the first joint of 

 the anterior antennae, and a slight corresponding one on the second joint of the second 

 antennas ; it is protected by a blepharis or fringe of hairs that traverses the orbital notch 

 of the carapace, the infero-lateral margin of the rostrum, and the upper distal surface 

 of the first joint of the first antenna.- 



The first antenna has the peduncle shorter than the rostrum. The first joint is long, 

 convex beneath, where it is armed with a sharp tooth at the inner distal angle, it is 

 depressed on the upper surface, being somewhat concave to admit the eye, and has 

 near its base a small, rounded, squamous expansion, furnished with cilia forming a row 

 continuous with that which fringes the outer margin of this and the two succeeding 

 joints ; the second joint is subcylindrical, and is scarcely one-third the length of the 

 first ; and the third is about half the length of the first ; the last tw r o joints are thickly 

 fringed with short plumose hairs on the lower angle of the inner margin ; the third 

 joint supports at its extremity two subequal filamentous appendages, which are twin 



