194 DE. C. CHILTON ON THE SUBTEEKANEAN 



se,^ment, the lower margin of the coxa being straight or somewhat concave. In the fifth 

 segment the coxa occupies only the posterior half of the lower margin of the segment, 

 but in the sixth and seventh segments, which are considerably shorter, the coxa 

 occupies nearly the whole of the lower margin. The basos is oblong, about twice as 

 long as broad, its slightly convex anterior margin supplied with eight or nine short but 

 rather stout setae and a tuft of finer hairs at the extremity ; the posterior margin 

 pioduced somewhat backward, as in the Aniphipoda, irregularly serrate, and armed, 

 except towards the extremity, with about a dozen strong spiniform setae. The ischium is 

 as long as the basos, its anterior margin straight, obscurely serrate, and with five small 

 tufts of setae marking the serrations, and a transverse row along the distal margin ; the 

 posterior margin is convex, with five serrations, each of the first four bearing a strong 

 spiniform seta, and the last a row of about four or five. The meros is rather more than 

 half as long as the ischium, the anterior margin straight and bearing three groups of 

 stout setae, the distal one being the largest ; the posterior margin bears two or three 

 spiniform setae, and a row of three or four along the distal margin at the posterior angle, 

 ^^ hich is somewhat produced. The carpus is as long as the propodos, but broader : both 

 are oblong, slightly expanding distally, with groups of stout setae along both margins, 

 but more especially along the anterior margin, and a row along the end at each angle. 

 The dactylos is about as long as the setae at the end of the propodos, similar to the 

 dactylos of the second pair of legs, but more slender. 



The pleopoda of Fhreatoicus are large and well developed, and present such pecu- 

 liarities that they are well worthy of careful examination and description. The five 

 pairs all appear to be branchial in function, and though the first pair differ in shape 

 from the others, they appear to be the same in minute structure, probably fulfil 

 the same function, and do not act as an " imperfect operculum " to the others as I 

 originally stated [23, p. 91]. All the pleopoda hang vertically from the ventral surface 

 of their segments, and are protected laterally by the greatly developed pleura. 



The first pair of pleopoda (PI. XVII. fig. 10) have the basal joint ov protopodite sub- 

 rectangular, with one seta at the extremity on the outer margin, and several similarly 

 placed on the inner margin. From the protopodite arise two rami, both long and 

 narrow ; the inner one, endopodite, is narrow-elliptical, aliout five times as long as broad, 

 with the margins quite entire and without setae, and the extremity subacute ; the outer 

 ramus, exop)odite,\9, oblong, longer than the endopodite, the inner margin nearly straight, 

 outer margin irregularly curved at each end ; the whole of the inner margin and the 

 extremity fringed with rather long setae ; on the outer margin the setae are long at the 

 end, but they become smaller toward the base and disappear altogether before the base 

 is quite reached. All the setae on the inner margin are simple, those at the extremity 

 and on the neighbouring portion of the outer margin are plumose ; the others on the 

 outer margin become gradually less plumose as they approach the base, until at about 

 the middle of the joint they are quite simple. 



The second pair of pleopoda (fig. 11) differ in the two sexes, being specially modified 

 in the male so as to serve as an accessory copulatory organ. It will be convenient to 

 describe that of the male first. The protojMdite has the same general shape as in the 



