Hi Ben, It's an Agallissus, there was a recent post of one. A. melaniodes Dalman, 1823. There are currently 6 species in this tribe and at least four are quite variable.
The larvae of Agallissus feed in dead petioles of palm fronds. The link here shows a live adult and a teneral adult which I collected in South Texas at a wildlife preserve in 2009.
Agallissus melaniodes Dalman,1823 is not a flat-faced longhorned beetle : genus Agallissus in tribe Agallissini (post belonging to Cerambycinae not Lamiinae)