502 W. WILLIAMSON AND C. D. SOAR ON BRITISH HYDRACARINA : 



Nymph. 



The nymph is about 0*70 mm. in length and about 0*65 mm. 

 in breadth. The palpi are pretty much like those of the imago 

 so far as the structure is concerned, but in re&pect to the number 

 and arrangement of the bristles there is a marked difference. 

 The first segment has none at all ; the second has two on the 

 extensor surface and one distal. The third segment has only 

 two long bristles, both distal, one on the extensor surface and 

 one midway on the inner surface. The distal extensor surface of 

 the fourth segment has only three short ones, in other respects 

 it resembles the imago. The provisional genital area does not 

 extend beyond the epimera. The surrounding ring, which is in 

 communication with the epimera anteriorly by a small sclerite, 

 has about six fine pores. The four acetabula are stijDitate. 



Var. britannica Sig Thor covers some British specimens which 

 have the posterior pair of acetabula about the length of the 

 second pair instead of much shorter as is usually the case (Zool. 

 Anz., xxix. 776). 



Var. vigintimaculata Sig Thor has presumably the same 

 characteristics as the variety of the same name under L. insignis 

 (ib. 786). 



Var. dorsalis Sig Thor has the middle distal bristle of the 

 inner surface of third segment placed more towards the extensor 

 surface (ib. 779). 



Var. italica Sig Thor. Specimens from Lake Maggiore have 

 the legs, epimera and palpi of a decided greenish -blue colour 

 (ib. 779). 



These latter forms are evidently local, but it is open to ques- 

 tion whether they have sufficient claim to be ranked as varieties. 



Lebertia porosa has been recorded for Britain and appears to 

 have a fairly wide distribution, as even Siberia has added its 

 quota to the recorded distribution. 



Larva. 



The outline is approximately oval, and measures about 

 0*3 mm. in length and 0'2 mm. in breadth. The body is dorso- 

 ventrally compressed, and this applies particularly to the posterior 

 region. The dorsum and venter are both protected, the former 

 by a chitinous plate, which extends nearly to the edge of the 



