On Fresh-water Entomostraca. 29 



In one of my aquaria there developed several specimens 

 of an llyocryptus, which I am unable to distinguish from 

 the well-known European species I. sordidus, Lièviu. In 

 order to show the identity of both forms, I have given on 

 the accompanying plate a figure of a full-grown female spe- 

 cimen, together with more highly magnified detail figures of 

 one of the antennulæ and of the tail. The specimens, which 

 exhibited a blood-red colour, did not exceed a length of 

 0,57 mm. 



As in most other species of the genus, the shell is not 

 completely cast off by the several exuviations of the animal, 

 and in fully grown specimens (fig. 1), therefore each valve 

 has the appearance of being composed of a more or less 

 considerable number of superposed valves of different sizes, 

 most of them still exhibiting their marginal setous armature. 

 It is chiefly on this account that the animal is generally found 

 so densely covered with mud as to be scarcely recognizable. 

 Indeed, the mud adheres so firmly to the numerous rows 

 of bristles, that it is a matter of great difficulty to cleanse 

 the shell sufficiently for a minute examination. The speci- 

 mens were only found on the bottom, more or less deeply 

 buried in the loose muddy deposit, through which they 

 moved very slowly by the aid of the antennæ and the 

 powerful tail. I have never seen the animal make even 

 the slightest attempt to lift itself from the bottom, and in 

 this respect it differs rather markedly from the 2nd Austra- 

 lian species, I. longiremis, which is by no means devoid of 

 swimming power. 



Occurrence. — The specimens were raised from the 

 same parcel of mud, which yielded the above-described 

 Moina temiicornis. As above stated, this mud was derived 

 from a pond at the corner of Bourke Street and Botany 



