Found on Youtube: Intro to Diamond Guard
I know this guy just makes you want to explode with Napoleon Dynamite references, but please don't. He looks like he knows what he's doing as he walks you through a position that's often passed over for more spider guard work in sport bjj.
I've been shown several setups from here, but never played with an overhook. Instead most people at my academy put both shins on the biceps and monkey paw each triceps.
Obviously this is designed for MMA, but I could see this being a useful addition to sport jits, especially in the situation where you've zombied one hand to the mat but your omoplata/jiu claw is being blocked because he's dropping his shoulder weight to that side.