NEBALIOPSIS 209 



marginal setae, from the thin plate-Hke epipodite of the first trunk Hmb. A still more 

 important difference is that these epipodites do not nearly cover the lateral gaps between 

 successive trunk Hmbs (Figs, i, 3). 



It may be conveniently mentioned here that it is a complete puzzle as to how a female 

 Nebaliopsis carries its embryos, if indeed they are carried. In all other Nebaliacea the 

 tips of the endopodites of the typical trunk limbs curve inwards and form a basket 

 under the trunk (compare Fig. 6 of Nebaliella) but this cannot be possible in Neba- 

 liopsis. 



The inner margin of these trunk limbs are armed with setae just as are the trunk 

 limbs oi Nebalia. On each limb there are two distinct sets. One row consists of very 

 long setae which extend forwards as far as the inner margin of the limb in front. The 

 second set is an irregular strip of minute setae which project inwards and touch the 

 tips of the long setae from the limb behind (Fig. 5 A). There is thus a zigzag of setae 

 forming, on each side, the wall of the median space between the limbs, but the setae 

 are not interlocked as in Nebalia. The first set are undoubtedly homologous with what 

 I have termed the first row setae of Nebalia (1927, p. 359). The second set may 

 represent the fourth row setae of Nebalia or may be the fourth and third rows 

 combined. 



The second trunk limb differs from the typical trunk limb in that its first row setae, 

 with the exception of the six proximal setae and two or three of the most distal, instead 

 of projecting straight forwards, project obliquely inwards and then curve backwards 

 (Fig. 4 C). The six proximal setae are shorter and project directly forwards. They 

 correspond to the gnathobasic setae of Nebalia. 



The eighth trunk limbs are very small and bear no setae. The main axis shows a 

 slight segmentation which probably separates off the distal endopodite. 



The pleopods and furcal appendages have been sufficiently described by Thiele 

 (1904, p. 23). 



From the account I have given of the arrangement of the limbs, it is obvious that the 

 feeding mechanism of Nebaliopsis must differ considerably from that of Nebalia. 



In Nebalia all the eight trunk limbs project almost at right angles to the body on 

 either side of a median space — the filter chamber. Their endopodites recurve sharply 

 backwards and slightly inwards so that their tips touch in the middle line. A floor is 

 thus formed to the filter chamber. The eighth trunk limbs interlock in the middle line 

 and so form the hind wall. The lateral walls are formed on either side by a continuous 

 series of interlocked setae borne on the inner margins of the limbs, two sets of setae on 

 each limb (the first and third rows) hooking into the setae of the limbs fore and aft. 

 Thus the only entrance to the filter chamber is anteriorly. Water is sucked in through 

 this opening by the rhythmical movement of the trunk limbs and caused to pass through 

 the filter walls between the trunk limbs to the exterior, the food particles being retained 

 in the filter chamber. The passage of water in one direction through this filter system is 

 made possible by the valvular arrangement of the exopodites and epipodites. On each 

 limb these structures form a complete valve closing the space laterally between that 



