479 



BRITISH HYDRACARINA: THE GENUS LEBERTIA. 



By W. Williamson, F.R.S.E., and Charles D. Soar, 



F.L.S., F.R.M.S. 



{Bead March 23rd, 1915.) 



Plates 33-34. 



In his posthumous memoir published in 1879, under the title of 

 " Description de quelques especes nouvelles d'Hydrachnides du 

 Lac Leman," * Lebert described a hydracarid which he con- 

 sidered to be new on account of the form of its genital area. 

 He gave it the name of Pachygaster tau-insignitus, and he 

 explained the specific name by referring to the resemblance 

 which the light dorsal marking bore to the Greek letter tau (t). 

 As to why he selected Pachygaster as a generic name, he has 

 left us in the dark. The selection, however, was not a happy 

 one, as Meigen used it in 1803 (Diptera), Germar in 1817 

 (Coleoptera) and Gray in 1840 (Echinodermata).f In the year 

 following the publication of Lebert's memoir, Neuman changed 

 the generic name to Lebertia. % One can without difficulty 

 comprehend how, from the lack of detail, several species were 

 identified as tau-insignitus ; and although some few species were 

 described by Koenike and Piersig, it was not until after Sig 

 Thor's exhaustive study of the genus that its comprehensive 

 character was recognised. The result was, that although 

 tau-insignitus had been naturally designated as type, the working 

 out of the species which had been identified as tau-insignitus led 

 to the creation of other species, so that, curiously enough, tau- 

 insignitus was worked out of existence altogether. Sig Thor 

 apparently recognised the illogical position which had arisen, for 

 we find that later on he, in company with the late Prof. Forel, 

 examined the locality at Morges where Lebert had obtained his 

 specimens at a depth of 25 m. They were successful there in 

 obtaining material which proved on examination to be quite 

 distinct from anything previously described. As other repre- 

 sentatives of the genus were not met with, one may conclude 



* Bull. Soc. Vaud., xvi. 327-377. 



f Nomen. Zool. Agassiz. 



% Kgl. Sv. Vet. Akad. Handl., xvii. (3) 68. 



