I’ve seen one set of photos extremely similar to this which it was identified as Mecynodera coxalgica & like yours it too was missing the usual solid yellowish lines on the pronotum, upper & mid elytra…. Completely black with only the yellow lines on the elytral shoulders and posterior. I just don’t know this group well-enough to say for sure, so I’ll Verify it at Genus-level with the Suggestion at Species-level.