ON SOME AUSTRALIAN CLADOCERA. 469 
A single specimen of this form was found at Kendall in 
October, and a number at Port Stephens in September. 
Sars records this species from Oentennial Park, Sydney. 
Genus ACROPERUS Baird. 
ACROPERUS AVIROSTRIS Sp. 0. 
(Plate XL, figs. 3, 4.) 
The length of the adult female is from 0°57—0°68 mm. 
The carapace is compressed, and viewed laterally, the 
shape is truncated oval; the greatest height is more than 
half the length and occurs in front of the middle. The 
dorsal margin is fairly strongly arched; the ventral edges 
of the valves are convexly curved in front, but straight for 
the remainder of their length; the posterior edges are 
obliquely truncated, slightly curved. The postero-dorsal 
angle is very obtuse, almost obliterated; the postero- 
ventral angle is distinct and bears two denticles on each 
valve. 
The head is bent down, the dorsal margin forming an 
even curve with that of the carapace. The rostrum is wide 
and blunt. 
The surface of the carapace is marked by a series of 
distinct oblique striations. The ventral margins of the 
valves are fringed with a row of long bristles. 
The eye is of moderate size; the ocellus is only slightly . 
smaller and situated closer to the eye than to the end of 
the rostrum. , 
The antennules are long and slender, reaching nearly as 
far as the tip of the rostrum; the tuft of sensory bristles 
at their apex extends beyond the rostral tip, 
The antenne are long and slender with long swimming 
bristles. There are three bristles and a spine on the ter- 
minal segment of the outer branch, and three bristles on 
