THE GENUS LEBERTIA. 485 



separated, while all the small hairs on the extensor surface are 

 distal. 



In the second group the skin is either not dotted over with fine 

 pores, or, where such are present, they are indistinctly seen ; but 

 a more distinctive feature is the presence of papillae or of ridges 

 varying in length. Species which are apparently smooth-skinned, 

 but belong to this group, may be distinguished from the preceding 

 group by the presence of six long bristles on the third segment of 

 the palpi instead of five. As a rule, swimming hairs are either 

 quite rudimentary or entirely wanting, but in some species, e.g. 

 those with six bristles on the third segment of palpi, they are to 

 be found. 



Three sub -genera, Mixolebertia, Pseudolebertia and Hexalebertia, 

 belong to this group. 



In sub-genus Mixolebertia the skin may be papillose or finely 

 granular, finely porose, rarely smooth. Swimming hairs are 

 generally present. The inner surface of the third segment of the 

 palpi possesses six long bristles, while as many as ten spines 

 may be found on the extensor surface of the first segment of the 

 fourth pair of legs. 



Pseudolebertia and Hexalebertia have certain characters 

 in common, in that they possess a skin which is apparently not 

 porose, but is coarsely papillated or covered with ridges of vary- 

 ing length, and that they are devoid of swimming hairs ; but 

 otherwise they may be contrasted as follows : 



In sub-genus Pseudolebertia the third segment of the palpi 

 has five long bristles, of which three are towards the distal 

 extremity. One or two more rarely three of the fine hairs 

 on the extensor surface of the fourth segment are more proximal 

 than the others. The anal aperture is devoid of an outer 

 chitinous ring. 



In sub-genus Hexalebertia the third segment of the palpi has 

 six long bristles. The fine hairs on the extensor surface of the 

 fourth segment are grouped about the distal extremity. The 

 accessory claw and lamina at the distal end of the sixth segment 

 of each leg are sometimes reduced in size. Anal aperture 

 surrounded by a chitinous ring. 



Fortunately material was available to enable Sig Thor to work 

 out the nymphal characteristics of the sub-genera. 



In sub-genus Pilolebertia, the nymph has a very finely 



