BY MARGUERITE HENET. 45 



eye and situated closer to it than to the tip of the rostrum. Post-abdomen com- 

 paratively slender, bearing numerous hair-like marginal denticles; end-claws 

 strong, each with two secondary denticles at the base. Length .6 mm. Colour 

 brown. 



Distribution. — N.S.W. : Only thus far from localities near Sydney, Ponds 

 near Lachlan and Bourke Sts., Waterloo Swamps, Botany. Victoria, South 

 Africa, South America, Hungary. 



Pleuboxus eeticulatus Henry. (Plate vii., figs. 2-2«..). 

 Proe. Roy. Soe. N.S.W., lii., 1918 (1919), p. 478. 

 Distribution. — N.S.W. : Port Stephens, Kendall. 



Pledroxus austealis, n.sp. (Plate vii., fig. 3). 

 Female. Carapace, seen laterally, comparatively long and low; dorsal mar- 

 gin evenly curved for the gTeater part of its length, but sloping abruptly down 

 to the posterior margin; ventral edges of the valves slightly convex; posterior 

 edges very short and truncated. The head is small and depressed, terminating 

 in a long acutely-pointed rostrum which projects slightly beyond the ventral 

 mai-gins of the carapace. The eye is large, the ocellus smaller, and situated 

 more than twice as far from the tip of the rostrum as from the eye. The sur- 

 face of the carapace appeai-s quite smooth, without any reticulation. The ventral 

 edges are fringed with a row of bristles which are finely ciliated. The infero- 

 posteal angle is an obtuse angle and is armed with 3 or 4 strong teeth. The 

 antennules are short and thick and do not extend to the middle of the rostrum. 

 The post-abdomen is moderately strong, tapering slightly distally, with the corner 

 opposite the end-claws produced forward, although not to the same extent as in 

 the preceding species, supra-anal angle obtuse, 14-16 anal denticles; end- 

 claws long and moderately strong, each bearing two denticles at the base. Colour 

 pale yellow, length .5 mm. 



The most nearly related species to this is i^erhaps the American form 

 Pleuroxus denticulatus Birge, but this species is very distinct from it in the 

 general shape, absence of reticulation and in the armature of the post-abdomen. 

 Distribution. — N.S.W. : Bangalow, Cumbalum. 



Genus Chydorus Leach, 1843. 

 Female. Body small and spheroidal. Head depressed, rostrum long and 

 acute. Lip-plate moderately large, narrowed posteriorly. Infero-posteal corner 

 usually unarmed. Antennules short and thick. Antennae provided with 7-8 

 swimming bristles. Post-abdomen short, supra-anal angle prominent; end-claws 

 with two basal spines. 



Male. Smaller, rostrum short, antennules thick, first foot with a hook. 

 Between thirty and forty species have been described from all parts of the 

 World, six of them occurring in New South Wales. 



Key to species of Chydorus. 



A. Infero-posteal corner with a spine unispinus. 



AA. Infero-posteal corner unarmed. 



B. Post-abdomen long and slender globosus. 



BB. Post-abdomen short and broad. 



C. Carapace strongly marked with oblique ridges jugosus. 



CC. Carapace smooth or weakly reticulated. 

 D. Olfactory setae all terminal. 



E. 15 anal denticles denticulatus. 



EE. Less than 12 anal denticles leonardi. 



DD. One olfactory seta lateral ovalis. 



