1888.] AUSTRALIAN CLADOCERA. 19 



a rather elongate spine, and has moreover on the exterior side 

 of its basal part 2 very delicate sensory bristles (see fig. 2), 

 affixed close together. The branches are nearly equal in size, 

 narrow cylindrical and composed, the lower of 3, the upper of 4 

 joints. The lower branch is provided with 5 slender Inarticulate 

 natatory setae, 3 of which issue from the tip. The upper branch 

 has only 4 natatory setae, 3 at the tip and one issuing from the 

 penultimate joint; on the other hand the antepenultimate join I is 

 armed at the extremity, outside, with a small spine. As shown 

 by Schoedeler, the upmost of the three apical setae of this branch 

 exhibits a structure essentially different from that of the others, 

 being considerably shorter and always curved upwards. On clo- 

 ser examination (see fig. 3) it is found to consist, like the other 

 setae, of a somewhat ticker basal portion tinely ciliated at both 

 edges, and a much narrower terminal part; but the latter is 

 quite smooth and terminates with a chitinous recurved point, or 

 hook. This seta represents a sort of clasping organ, by means 

 of which the animal can cling to aquatic plants or other sub- 

 merged objects. 



The oral parts and legs do not exhibit any essential diffe- 

 rence as to structure from those parts in other species of the 

 genus. 



The tail (fig. 4) is very broad, lamellar, and as a rule 

 strongly infiexed or doubled upon the preceding part of the body, 

 being thus wholly covered by the valves. It is however very 

 mobile and admits too at times of being exserted far beyond the 

 carapace posteriorly. Its ventral edge exhibits close to the base 

 a sharp curve, but for the rest is quite straight and smooth. 

 The dorsal edge, on the other hand, is irregularly flexuous, its 

 outer part forming along the anal fissure a rather deep sinus, 

 bounded posteriorly by an obtuse angle, anteriorly by a slightly 

 projecting curve bearing the anal denticles. Just posterior to 

 the above-mentioned supraanal angle, it bulges out a little, ter- 

 minating in a notch, that indicates the limit between the tad 

 and the adjoining part of the body. Immediately below this 

 notch the two rather small caudal setae originate. The caudal 



