1888.] AUSTRALIAN CLADOCERA. 57 



The adult male (fig. 3) is much smaller than the female, 

 its length reaching only 0.34 mm. The carapace is somewhat 

 more regularly quadrangular, being more distinctly truncated 

 posteriorly, and having the dorsal edge but very slightly arched. 

 The inferior edges of the valves, too, ascend considerably in 

 their anterior part, whereby their edges appear almost an- 

 gular just anterior to the middle, and, finally, the sculpture of 

 the shell is much less pronounced. There are however some 

 other characteristics, by which the male differs much more mar- 

 kedly from the female. Thus, the antennulae are much larger 

 and project considerably beyond the tip of the rostrum, the 

 latter appearing comparatively shorter and more obtuse. More- 

 over, the 1st pair of legs are armed with a powerful, anteriorly 

 curving hook, projected beyond the inferior edges of the valves. 

 Finally, the tail (fig. 4) exhibits a very different aspect, being 

 comparatively shorter and less strongly compressed, as also al- 

 together wanting the dorsal denticles, only the lateral rows of 

 delicate spines being left The supraanal angle is well marked, 

 as in the female, but the extremity of the tail rather different, 

 being almost transversely truncate and having about in the 

 middle a small knob-like projection, to which the caudal claws 

 are attached; the latter, moreover, occur considerably shorter 

 than in the female, though exhibiting the secondary denticle at 

 the base. 



The testes, located on either side of the intestinal tube, 

 the loops of which they partly cover, are divided into several 

 saccular compartments, connected by narrow passages; posteriorly, 

 just at the flexure between the body and tail, the testes contract 

 to a narrow canal running close to the ventral edge of the tail 

 and disembouching at its tip, immediately in front of the caudal 

 claws. 



The colour of the male is always much paler than that of 

 the female, the whole body being very pellucid and but faintly 

 tinged with yellowish. 



Biological Observations. — Of the present Lynceid I have 

 been enabled to examine numerous specimens, both males and 



