The suprageneric diagnosis follows Puckett (2002). Brachycythere smithsoniana sp. nov. presents the very distinctive feature among species of Brachycythere of having differences in ornamentation between its left and right valves as following: the right valve presents three weakly distinguishable ribs in dorsal, central and ventral positions, while the left is smooth. Brachycythere asymmetrica Puckett, 1994 also has dissimilar ornamentation between its left and right valves, but in a different pattern: in this species, only a ventral rib is present and this in both valves, although developed in varied levels from left to right; it is also distinct between male and females of the species (Puckett 1994). Veenia GAD 34 in Grosdidier (1979) is co-specific to Brachycythere smithsoniana sp. nov.
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