1885]. 



CLADOCEEA. 



41 



stitutes a pellucid triangiilar lobe, without any armature of setæ 

 or spines, finely ciliate along the inner edge only. The exopod, 

 on the other hand, is prodigiously developed, in the form of an 

 exceedingly large rounded plate, finely ciliate round the edges, 

 and provided also in the exterior part with 4 strong plumous 

 setæ of nearly equal length. As in the preceding pair, a thin 

 ciliated lobe projects immediately above the small rounded epipod. 



The tail (see Pl. 7, fig. 1 ; Pl. 8, fig. 7) has the dorsal part, 

 where it is connected with the trunk, strongly projecting — to 

 close up the matrix behind, and exhibits posterior to this projection, 

 3 bunches of delicate bristles, affixed to the end of as many 

 separate segments. The terminal section, connected as usual 

 with the proximal part of the tail by a very mobile articulation, 

 is exceedingly large, forming a broad vertical plate, the dorsal 

 margin of which is evenly arched. It tapers a little toward the 

 apex, which exhibits an angular incision bounded anteriorly by 

 a short conical process (to which -the caudal claws are affixed), 

 — posteriorly, by a well-marked, almost right-angled corner. 

 The dorsal edge of the caudal plate is quite unarmed, being 

 furnished merely with a very delicate ciliation. On the other 

 hand, a lateral series of close upon 20 very slender, well-nigh 

 setiform spines occur at some distance from the edge, increasing 

 successively in length toward the apical angle, and projecting 

 more or less beyond the dorsal edge. At the base of each spine, 

 is observed moreover an oblique series of 2 or 3 much smaller 

 spinules, and in some examples there would even appear to be 

 several such series. But, when such is the case, it may be safely 

 alledged that, on closer examination, such specimens will be found 

 about to moult, and also that the apparent increase in the number 

 of spines arises simply from those in process of development — to 

 take the place of the old ones after moulting — becoming visible 

 beneath the integument. The apical claws are very long and 

 slender, only slightly curved, and quite smooth, without the slight- 

 est trace of a basal tooth. The caudal setæ, affixed to a short 

 process close to the joint connecting the caudal plate with the 



