40 FRESHWATER EKTOMOSTEACA OF N.S.W. 1. CLADOCERA, 



Genus A l o n a Baird, 1850. 



Body more or less compressed, in lateral view oval-triangular or oval-rect- 

 angular with rounded posterior angles. Head not carinate. Process of the 

 upper lip often large, rounded. Antennules short and thick. Antennae short, 

 the inner ramus with 4 or 5 swimming bristles. Five to six pairs of legs, the 

 sixth, if present, rudimentary. Post-abdomen compressed, armature varied, 

 usually both marginal denticles and lateral combs present; end-claws with one 

 basal spine. Over seventy species have been described from all parts of the 

 World, eleven of which are included in the fauna of New South Wales. 



Key to species of Alona. 



A. Length exceeding ,6 mm. 



B. Carapace smooth longirostris. 



. BB. Carapace longitudinally striated. 



C. Twelve anal denticles kendallensis. 



CC. Fifteen anal denticles. 



D. Post-abdomen of uniform width affinis. 



DD. Post-abdomen widening distally wluteleggii. 



AA. Length not attaining .6 mm. 

 B. Lateral fascicles absent. 



C. Ocellus equal in size to the eye clathrata. 



CC. Ocellus much smaller than the eye. 



D. Supra-anal angle very distinct abbreviata. 



DD, Supra-anal angle not distinct microtata. 



BB. Lateral fascicles present. 



C. Fascicles long, e.xtending beyond the dorsal margin . . . . cambouii. 



CC. Fascicles short, 



D. Post-abdomen long and slender wallaciana. 



DD. Post-abdomen short and stout, 



G. Carapace striated .. pulchella. 



EE. Carapace smooth laevissima: 



Alona affinis (Leydig). (Plate viii., flg-s. 2-2a.). 

 (Syn. Lynceus quadrangularis Fischer, not Muller; Alona oblonga P. E. Muller.) 



Described by Leydig in 1860 (p. 223) as Lynceus affinis. 



Female. Carapace, seen laterally, oval in outline, dorsal margin arched, 

 curving abruptly downwards posteriorly so that the greatest height is about the 

 middle. Ventral edges slightly curved, posterior edges obliquely truncated. Head 

 slightly depressed, rostral end pointing obliquely forwards. Eye large, ocellus 

 smaller, situated about twice as far from the rostral tip as from the eye. Sur- 

 face of the carapace marked by longitudinal striations which are not very con- 

 spicuous, sometimes a faint reticulation. Post-abdomen strongly built, of uni- 

 form breadth throughout; 13-15 serrated anal denticles; lateral combs present; 

 end-claws strong, each armed with a secondary denticle at the base; both end- 

 claws and denticles bearing spinules. Colour yellowish-brown, sometimes with a 

 greenish tinge. Length 1 mm. 



Distribution. — This is a very cosmopolitan species. N.S.W. : Centennial 

 Park, Lett River, Kendall, Byi-on Bay; Europe, Asia, North and South America, 

 Africa, Greenland, Siberia. 



Alona whiteleggii Sars. (Plate viii., figs. 1-la.). 

 Described by Sars (1896) from a single specimen obtained at Centennial 

 Park, Sydney. 



