A RARE HVDRACARIP LEBERTIA DENSA, KOEN 271 



A RARE HYDRACARID LEBERTIA DENSA, 



KOEN. 



By Wm. Williamson, F.R.S.E. 



Since Lebertia densa was described by Koenike in 1902 

 (Zoo/. Ans., xxv., 611) I have not seen any reference to its 

 distribution other than Harburg, where it was found. Its 

 occurrence at Craigallian Loch, where I took it at an 

 excursion of the Glasgow Microscopical Society in September 

 191 1, extends its recorded distribution and adds another 

 species to the Britannic fauna, bringing the number of our 

 Lebertia species up to eleven. 



In 1905 Thor placed L. densa provisionally in subgenus 

 Neolebertia, but in 1907 he transferred it to subgenus 

 Mixolebertia ; looking to the fact that Koenike said so little 

 about the palpi, I imagine that Thor had seen the type 

 before he finally placed L. densa in subgenus Mixolebertia. 



Compared with Thor's critical " Lebertia-studien," 

 appearing from time to time in the Zoologischer Ameiger, 

 Koenike's description is by no means as complete as is 

 desirable in this difficult genus, and is without figures. The 

 following description and figures will, I hope, bring this 

 species into line with Thor's studies of the genus. 



The body of L densa is about 1 mm. in length, and in 

 outline tends to be round. The skin is stout and is closely 

 covered with fine pores. As the surface ridges are so fine 

 and so wide apart, the skin might be almost classed as 

 smooth. The gland areas, which are relatively few in 

 number, are reddish brown and strongly chitinised. 



The capitulum is about 0-25 mm. in length. Compared 

 with the postero-lateral process, the antero-lateral process is 

 by much the stouter in build. Its outer half is of about 

 equal thickness throughout and ends bluntly. The postero- 

 lateral process is rather more than half the length of the 

 other and curves well round to the sides, ending in a point. 

 The pharynx is relatively broad, with its posterior end 

 71 2 H 



