42 Ct. O. Sars. 



The antennæ are of normal appearance, not being of 

 any unusual size. . 



The lamellar expansion of the labrum is rather large, 

 and exhibits in front a distinct notch not found in the 

 other known species. 



The tail (fig. 6) is short and thick, on the whole 

 resembling in shape that in A. macrocopa, though having 

 the tip less obliquely blunted, and the rounded posterior 

 corner more prominent; around the latter, a double series 

 of from 8 to 10 well-defined denticles occur. The post-anal 

 angle, as in A. macrocopa, is rather prominent, and placed 

 nearly in the middle of the posterior edge. 



The colour in living specimens is yellowish, or pale 

 corneous. 



Observations. — This form developed rather plenti- 

 fully in one of my aquaria, and during one period of the 

 season, it occurred in such numbers, that I was almost sure 

 to get some specimens, on taking up, by the aid of a dip- 

 ping tube, a very small portion of the loose bottom deposit, 

 and examining it in a watch-glass. In the latter part of the 

 summer, however, it almost wholly disappeared, and no male 

 specimens were for this reason secured. It moves through 

 the water in the very same manner as most other species 

 of the genus, the movement being quite even and somewhat 

 tremulous, not, as is the case with the New Zealand spe- 

 cies, by abrupt jerks. 



Occurrence. —The mud from which this form was 

 raised, was taken by Mr. Whitelegge from a pond at the 

 corner of Bourke Street and Botany Bay. The species also 

 occurred in a sample from the same locality, but in a very 

 limited number. 



