No geographic variation noted in external features. However, the length of the second stylomere in females varies considerably, with specimens from north of Bandon, Oregon, having much longer stylomeres than specimens in northern California.
Comparison with Related Species
For a discussion of the traits distinguishing B. zephyrum from B. levettei, see Separating B. zephyrum from B. levettei.
Male genitalia with Ventral Sclerite Patch usually without the distinctly angulate and sclerotized dorsal ridge of related species.
Adult External Characteristics
A wide, flat species, with extensive, distinct mirrors. Anterior mirrors of elytra connected to rest of mirrors only by fainter mirrors on interval 3. Midlateral pronotal seta present.Lateral margin of prothorax explanate, especially toward the prominent front angles: