1889.] ON SOME FRESHWATEK OSTBACODA AND COPEPODA. 61 



wards between the insertion of the anterior antennae and bears 

 at the tip 2 exceedingly small tentacular appendages. 



The posterior division of the body, or tail (see figs. 12, 13 

 and 16) does not attain the third part of the length of the 

 anterior, and is also much narrower. It apparently consists only 

 of 2 segments, besides the furcal lobes. The anterior of these 

 segments is by far the larger and about equals the whole remain- 

 ing part of the tail. It is nearly cylindrical in form, or but 

 very little dilated in its basal part and does not exhibit any 

 trace of the usual lateral projections; in their place only an 

 extremely small and delicate bristle may be detected springing 

 off from a shallow pit. Ventrally this segment exhibits near 

 the base the usual obtuse protuberance containing the genital 

 orifice (see fig. 13). The posterior segment comprises properly 

 speaking no less than 3 originally distinct segments, which 

 however in the adult female become completely fused together and 

 are only indicated by a very slight folding of the lateral edges 

 (see fig. 16). In the posterior part this terminal segment is a 

 little dilated and somewhat flattened, with a slight median 

 incision. Somewhat in front of the latter on the dorsal side 

 a semilunar transverse fold occurs, covering over the anal 

 orifice, and from either extremity of this fold a slightly curved 

 line extends posteriorly, limiting the anal area. The furcal 

 lobes are rather broad, subquadrangular, or slightly dilated 

 towards the tip; their inner edge is finely ciliated, whereas the 

 outer edge has a well-marked ledge in the middle. The caudal 

 set* are 6 in number on each furcal lobe. The innermost of 

 these setae is however rather small and extremely thin, origi- 

 nating somewhat dorsally. The 5 other setae, on the other hand, 

 are very large and densely plumose, diverging to each side and 

 forming together with those on the other furcal lobe a broad 

 f an. which constitutes a most powerful propelling organ. Of 

 e setae the 4 originate close together from the truncated 

 extremity f the lobe, whereas the 5th is attached at some 

 Stance from the others to the ledge of the outer edge. All 



