Found living inside older specimens of a finned tree fungus species. To my naked eye (well okay, assisted by prescription eyeglasses), this species appeared identical to Octo*temnus lae*vis. However, reading as I have that ciids are highly host specific, I was keen to see what these guys looked like under maximum magnification. Sure enough, they are a different species -- way different!

These should be easy for a specialist to ID in view of their double "horns" on both the pronotum and rostrum, not to mention their ruby-hued faces.

These beetles had eaten tunnels crossways through the fins, sort of like a tiny bullet hole through the pages of a book. Some appear to have larger horns and they might be males. The males in at least some horned species are said to fight with each other in their tunnels, over females no doubt.