Two new species of Hydrodessus from Suriname, with a key to the known species (Coleoptera: Dytiscidae)

The genus Hydrodessus is readily distinguished, from the other small water beetles related to the Old World Bidessus, by the lack of pronotal or elytral plicae, by the structure of the hind coxal processes, and by the simple, unjointed parameres of the male genitalia (Balfour-Browne, 1953). The species are very rare in collections, and several are still known from only the unique types. The genus Brinkius (Guignot, 1957) differs from Hydrodessus only in that a fine lateral humeral carina is present on the elytron above the epipleural margin. In all other characters, including the unique parameres of the male genitalia, the two genera seem to be identical, and I therefore apply the older name to both groups. The two new species described below from Suriname extend the range of this genus north of the Amazon basin. All the previously described species are from Brasil or the Amazonas region of Perú. The species from Perú were described by Spangler (1966). Of these, Hydrodessus nanayensis is exceedingly similar to the genotype H. siolii Balfour-Browne described from the state of Pará, Brasil. I believe these will prove to be subspecies at most although the type localities are separated by over 1500 miles.