﻿224 Proceedings of the Royal Physical Society. 



any definition to the genus until the appearance of his 

 "Ubersicht" in 1842. Here he defined Atax differently 

 from Duges, giving to the name the definition which was 

 extended by Bruzelius in 1854, and this remained un- 

 challenged until Oudemans and Wolcott took up the position 

 referred to. 



It is evident that Fabricius considered Atao:, for which 

 he designated no type, as an equivalent of Hydrachna Miill., 

 since he quoted the latter as a synonym. Hydraxhna Miill., 

 being the older name, has a right to priority, to which, 

 moreover, Latreille's genera are also entitled, both on 

 account of their earlier date as well as for their designation 

 of types. Apart from these considerations, however, it is 

 to be observed that Atao^ (F.) Duges, is invalid as none of 

 the species originally included in the genus were included 

 by Duges in the restricted genus. 



Since Atax F. is invalid, it cannot be longer retained as 

 a generic name. As pointed out by Oudemans and by 

 Wolcott, there is no choice but to give to the genus to 

 which C. L. Koch, and later Bruzelius, gave the definition 

 it now bears, the name of Unionicola Hald., and the generic 

 name of our British species must be changed accordingly. 



Wolcott selected from Haldeman's species U. oviformis 

 as typical, and as it appears to be the species named 

 Hydrachna y^gsilo'phora by Bonz, the type of the genus, as 

 designated by Wolcott, is Unionicola ypsilophora (Bonz). 



