A?i account of some hitherto unnoticed species of 

 the genus Hydrachna, Miiller. 



Genus? Unionicola.* [Fam. Hydrachnid^.] Corpus 

 oviforme, pedibus ingequalibus: palpi conici, inflexo-arcuati, 

 et articulati; apicibus acutis. (PI. 1.) 



1. . . . oviformis. (Fig. 1-5.) Margins and 

 legs pale ochraceous, upper surface black, with 

 a white or yellowish central, longitudinal line, 

 which bifurcates anteriorly. Hab. Unio radia- 

 tus, Gmelin. 



2. . . . lactea. (Fig. 6-8.) Like the pre- 

 ceding, but with the white of the upper surface 

 much more extensively spread, and the black 

 replaced by dark brown. The posterior ex- 

 tremity is slightly produced. Hab. Unio cariosa, 

 and Anodon cataractus. Say. Perhaps a variety 

 of the preceding. 



* This name may be preferred by some in an ab- 

 breviated form, as Unicola. 

 1 



