KEPORT ON THE PHYLLOCARIDA. 17 



number of segments. These segments are, however, ver}^ imperfectly defined, and hence 

 can only be exactly counted with great difficulty, except on the posterior pairs (fig. 4), where 

 they appear more distinct, amounting to six in all. The inner edge of the stem does not 

 show any trace of lateral lobes or endites, but is bordered by a regular series of rather 

 elongate and slender ciliated setae. Besides, at a short distance from the edge along the 

 posterior surface, another similar series of slender setas occurs, and this series on the last pair 

 (fig. 4) successively passes over from the posterior surface to the outer edge, whereby the 

 terminal part of the endopodite becomes densely setiferous on both edges. Finally, a 

 third series of very minute hair-like bristles is found close inside the latter series along 

 the posterior surface of the legs. The setce of the basal part in all the legs are considerably 

 shorter than those affixed to the endopodite, though arranged in a similar manner. The 

 apical setas in most of the logs (figs. 2, 3) differ somewhat from the rest, at least in the 

 female, one of them being densely plumose, whereas the others are quite unciliated, very 

 slender and strongly curved at the tip. On the last pair (fig. 4), however, the apical setae 

 do not differ materially from the lateral, but on close examination a very small spine, some- 

 what reminding one of the terminal claw in higher Crustacea, is found at the tip between 

 the setae. The exopodite, issuing from the base of the endopodite on the outer side, exhibits 

 an appearance very different from that in Nehalia, ha\dng the form of a slender plate, 

 somewhat shorter than the endopodite, and produced at the end into a very narrow flap. 

 It is fringed alono- its whole outer edo'e with a siuo;le regular series of slender ciliated 

 bristles, one of which issues from the tip. In the middle pairs (fig. 3) the exopodite is 

 very elongate, and beyond the middle more or less distinctly geniculate, with an approach 

 to a division into two parts, a basal and a very narrow terminal part, thus acquiring 

 a certain resemblance to the natatory branch in higher Crustacea. In the posterior pairs 

 (fig. 4) the exopodite becomes considerably shortened, and of a more simple form. The 

 epipodite, w^hich in Nehalia is exceedingly large and expanded both superiorly and inferiorly, 

 is in the present form reduced to a very small appendage affixed externally to the end of 

 the basal part. It has the form of a narrow recurved plate, very delicate in structure and 

 finely ciliated along the outer edge. In the anterior pair (fig. 2) this plate is slightly 

 bilobed, the inferior lobe being, however, very short and rounded ; in the succeeding pairs 

 (fig. 3) it is more simple and olilong in form, and in tlie last pair (fig. 4) the plate is 

 considerably more produced above than in the other pairs, forming a narrow, slightly 

 flexuous flap, which projects upwards beyond the base of the leg (sec PL I. fig. 1). 



The four succeeding pairs of limbs (PL I. fig. 1, p/; PL IL figs. 5-7), affixed to the 

 pleon, constitute very powerful natatory organs or ploopoda, which admit of being moved 

 with great force from before backwards, acting in nuuli the same manner as the swimming 

 legs in the Copepoda. They consist each of a broad and somewhat flattened basal part, 

 to the end of which two diverging linear branches are affixed. The basal part is strongly 

 muscular, and composed of two unequal segments, the proximal quite short, the distal 



(ZOOL. CHALL. EXP. — PABT LVI. 1887.) Kkk 3 



