REPORT ON THE CUMACEA. 17 



The greater part of this apparatus constitutes a very hirge membranous plate of a 

 somewhat navicular form, and curved so as to exhibit an outer convex and an inner 

 concave surface. It terminates in a recurved acuminate lappet, and is furnished along 

 the inner edge with a regular series of lamellar gill-lobules, increasing in size anteriorly, 

 the foremost of which is tui'ned backward. The whole plate is moved in the living 

 animal by an assemblage of strong muscles partly passing from the base of the corre- 

 sponding maxilliped. Anteriorly another smaller plate is seen extending forwards 

 and forming an imperfect funnel ; it tapers to a narrow band-like ligament, and 

 terminates in an indurated lamella armed with six curved setse, and encircled by a 

 very thin and pellucid border (fig. 13). This terminal lamella, which is distinctly 

 marked off from the plate by a transverse suture, is found projecting in front of the 

 pseudorostral prominence in close juxtaposition to the corresponding one of the other 

 side, and in living specimens both lamellas are seen performing a peculiar snapping 

 movement, whereby the water is expelled at intervals from the branchial cavities, during 

 the rhythmical strokes of the true branchial plate. Although this anteriorly directed jalate 

 would seem to be partly connected at its base with the principal plate, I am still disposed 

 to entertain the assumption I have set forth in another work,^ that the former is the 

 highly modified exopodite of the maxillipeds, whereas the latter represents the epipodite. 



Of the limbs of the trunk the two anterior pairs are closely a^Dplied against the oral 

 parts, and do not seem to have any locomotory function, and they may, therefore, proj)erly 

 be termed gnathopoda. These two pairs differ materially from each other both as regards 

 size and structure. 



The first pair of gnathopoda (fig. 14) form simple stems, composed of the sa.me 

 number of joints as the maxillipeds, but are rather more slender. The basal part is 

 longer than the terminal and somewhat laminar, with a slight longitudinal keel running 

 along the upper surface and terminating posteriorly in a dentiform projection of the outer 

 edge. This part, as in the maxillipeds, chiefly consists of a single joint (the basal), the 

 coxal joint being very small and imperfectly defined. It is furnished at the end with a 

 rather strong ciliated seta, and has, moreover, a few bristles at the outer part of both 

 edges, those of the exterior edge being larger and about eight in number. The first 

 joint of the terminal part is quite short and somewhat swollen, almost globular, with a 

 single bristle at the end on the outer side; the succeeding joint is a little longer, con- 

 stricted at the base, and furnished along the inner edge with several ciliated bristles, and 

 a single one at the end exteriorly. The two last joints are rather small, and beset with 

 bristles at the end. At the base of each of these gnathopoda there is afiixed, in the adult 

 female of all Cumacea, a lamella edged with very long setae projecting within the marsupial 

 pouch. This lamella was, however, only slightly developed in the specimens of the 

 present species, owing to their being not full-grown. 



' Beskiivelse af de paaFregatten Josephine's Expedition fundne Cumaceer. 

 (ZOOL. CHALL. EXP. — PAET LV. — 1886.) Ill 3 



