On Australian Entomostracans. 259 
abdomen is small, and the dorsal edge much sinuated. 
The two Ephippial eggs, «which are globular, are placed 
side by side, and seen through the back when the animal 
is placed on its anterior margin ; when seen in profile they 
appear but one. This species is smaller than the pre- 
ceding, and is very lively in its motions. It sometimes 
comes to the surface of the water, and remains there sta- 
tionary for a considerable time. I have observed the 
same habit in Hurycercus Cunninghami ; but it is not easy 
to discover much of the habits of species so minute that 
the aid of a magnifying glass is often required to detect 
even their presence. Chydorus Leonardi, on the under 
surface of the water and motionless, is certainly not a very 
striking object to the unassisted eye. I have found it a 
convenient test for deciding upon the powers of vision 
possessed by my friends. 
Habitat.—Sydney, near Waverly Mills; the Waterfall, 
St. Leonard’s; South Creek; Denham Court, &c. 
Genus Atona. (Baird.) 
“Shell quadrangular shaped, grooved or striated longi- 
tudinally. Inferior antennz or rami short. Beak short 
and nearly erect.” 
(1.) A. Bairdit. (Plate VIII. A.)—Carapace nearly 
quadrangular, anterior margin sinuated and ciliated. The 
abdominal margin notched. Rami with a long seta from 
each of the first two articulations of the posterior branch, 
three setz and a short spine at the extremity of the third. 
The anterior branch has also the same number at its 
extremity. In each of the sete, at the extremity, the 
first joint is produced into a spine, and the sete are plu- 
mose. ‘The last segment of the abdomen is much sinuated 
near the joint. 
