578 



Mrs. e. w. sexton on the 



(Through some mischance, Norman's figure of the first gnathopod 

 ((36) pi. ix. fig. 2) shows the second sideplate attached instead of the 

 first.) The first sideplate is subquadrate in the young animal, with 

 1 long sensory spine inset at the anterior angle, but with growth 

 this angle becomes more produced downwards, until in the largest 

 specimen of all the anterior margin of the sideplate is half as long 

 again as the hind margin. Four stages of development are 

 represented in the figures. The ' Huxley ' specimen forms the 

 link between figs. 14 & 15 ; the anterior angle is not so much pro- 

 duced as in the latter, 6 setules are inset anteriorly, 1 inferiorly, 

 and 3 short sensory hairs at the posterior angle. In Grube's 

 specimens, the anterior margin is lightly concave and the posterior 

 angle has a strong chitinous margin. The hinder poi'tion of the 

 sideplate is firmly afiixed to the basal joint beneath, so firmly in 

 fact as to make it impossible to separate them without destroying 

 the shape of the sideplate. A delicate laminar plate extends 

 beyond the sideplate behind, and is all but continuous with it 

 proximally, the line of demarcation being barely distinguishable. 

 Sideplate 2 is the largest of all, as deep as broad in the small 

 specimens, a little deeper than broad in the fully developed 

 animal ; front margin rounded ; hind margin almost straight with 

 4 small setffi inset ; inferior margin rounded, thickly fringed 

 with delicate, sensory, cleft-tipped setae of varying lengths 

 (26 in the young, to about 41 in the full-grown). The remaining 

 sideplates are very like those of the type species. Sideplates 3 

 and 4 are subequal to each other in length, shorter, than the 2nd, 

 about half as deep again as broad. The 3rd is of equal width 

 throughout, front and hind margins straight, the latter with three 

 or four setfe inset ; inferior margin convex, fringed with 10-19 of 

 the sensory cleft setfe. The 4th is a little wider proximally than 

 the 3rd, and the front mai'gin is lightly convex ; inferior margin 

 Avith fewer sensory setae, 5-15. In sideplate 5 the anterior lobe is 

 about as broad and as deep as the preceding sideplate ; inferior 

 margin rounded, with only 4-7 sette ; posterior lobe very small, 

 only one-third the depth of the anterior, 2 small seta? inset, 

 Sideplate 6 small; posterior lobe about half as deep as the 

 anterior, with 1 small seta behind and 1 of the sensory 

 serrate spines similar to those found on the hinder perteopods 

 and uropods (see fig. 21); on the anterior lobe are 2 ciliated 

 hairs. Sideplate 7 small and subquadrangular. 



Pleon. — Segment 3 much the longest, as long as the 1st and 2nd 

 taken together ; 4th segment a little depressed dorsally. The 

 hind margin of the 2nd is straight, that of the 3rd rounded; 

 inferior margins of 1-3 thickly beset with long plumose seta?, 

 most numerous on the 2nd. On either side of the median line of 

 the 4th and 5th segments the posterior margin is produced in an 

 erect membranaceous lappet-like process, too delicate in structure 

 to be termed a tooth, each process having a setule inset in the 

 notch (fig. 26). Both Costa and Grube refer to these setules, 



