486 W. WILLIAxMSON AND C. D. SOAR ON BRITISH HYDRACARINA : 



ribbed skin dotted with fine pores. The epimeral area is rela- 

 tively broad, with the provisional genital area lying well within 

 the genital bay. The two long bristles on the extensor surface 

 of the third segment of the palpi are distal, as well as the small 

 hairs on the extensor surface of the fourth segment. 



Sub-genus Lebertia also has a finely ribbed skin, dotted with 

 fine pores, but the epimeral area is relatively narrower and 

 longer, while the provisional genital area is set well back, 

 sometimes quite outside of the genital bay. Of the two bristles 

 on the extensor surface of the third segment of the palpi, one is 

 about the middle of the segment and the other distal. 



Sub-genus Mixolebertia has the skin strongly ridged and three 

 bristles on the third segment of the palpi. 



Sub-genus Pseudolebertia has the skin ridged, but more 

 sparingly than in the imago. The third segment of the palpi 

 has only two long bristles. 



Sub-genus Hexalebertia has the skin similar to Pseudolebertia, 

 but the third segment of the palpi has three long bristles, one of 

 these being much more proximal than the others. 



Sig Thor has also proposed to establish the sub-genus Duro- 

 lebertia to cover L. solida, but as that species appears to rest 

 on material hot too well preserved, the validity of Durolebertia 

 must remain open until further material is available to prove 

 its claims. 



It may be here observed that American writers do not appear 

 to favour subdivisions as outlined above. 



As the long bristles on the third segment of the palpi are an 

 important feature in the imago, the position of these on the 

 type species of the sub-genera may be approximately represented 

 as follows : 



< 



Lebertia. Pilolebertia. Mixolebertia. Pseudolebertia. Hexalebertia. 

 L. tau-inslgnita. L. insignis. L. brevipora. L. glabra. L. stigmatifera. 

















