1888.] AUSTRALIAN CLADOCERA. 47 



Gen. Alonella, G. 0. Sars. 

 7. Alonella diaphana, (King). 



(PI. 5, fig 8 . 5-7;. 



Alona diaphana, King, On Australian Entomostracans, 1. c. 

 p. 360. PI. VIII. C. 



Specific Cliaracters. — $. Carapace much compressed, as 

 seen laterally rounded oval, slightly tapering posteriorly, edges 

 everywhere rounded, without any angle posteriorly either above 

 or below. Head decumbent, hood-like, rostrum obtuse. Shell 

 arcuately striate, striae rather close together and partly ana- 

 stomosing, on the anterior part of valves obliquely ascending. 

 Eye of moderate size, crystalline lenses very minute; ocellus 

 somewhat smaller than eye, located about midway between that 

 organ and the tip of the rostrum. Tail rather large, oblong in 

 form, somewhat tapering distally, dorsal edge slightly arched in 

 the outer part and armed with very small, hair-like denticles, 

 supraanal angle ilight, apex somewhat produced anteriorly; cau- 

 dal claws rather strong, with a small secondary denticle at the 

 base. Body very pellucid and almost colourless. Length of 

 adult female 0,49 mm. 



llemarhs. — 1 think my identification of this form will also 

 prove correct; at least the general form of the shell agrees 

 rather closely with the figure given by King, and also its great 

 pellucidity would seem to strengthen this opinion. Mr. King 

 refers this species to the genus Alona Baird, but I feel per- 

 suaded, that both this and the following species ought more pro- 

 perly to be classed within the genus Alonella, as long since 

 characterised by the author. The striation of the shell in both 

 Offers materially from that in any species of Alona, agreeing 

 °n the other hand with that characteristic of the former genus. 



Desertion. — The length of the adult female is not quite 

 half a millimeter. 



The carapace is rather much compressed, though its dorsal 

 Part in ovigerous females becomes somewhat distended by the 

 enclosed eggs or embryos. As seen laterally (PL 5, fig. 5), it 



