The following key utilizes features of adult structure. The differences
in external structure between some of the species are rather subtle
(e.g. between B. balli and B. foveum). For these, an examination of
the male genitalia is sometimes necessary for accurate identification.
A page 
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comparing male genitalia may
be of use while examining genitalia.
(There is an alternative key with all couplets on one page.)
1. Distinct smooth patches ("mirrors") on elytra, at least on
interval 3 surrounding silver spots, or elytra generally
smooth and shiny ............................................3
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1'. Distinct elytral mirrors lacking, interval 3 between silver
spots dull, or at least not markedly shinier than rest of
elytra ......................................................2
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