It's a pickup that was developed by Hagstrom in the 60s and looks like the ones above, with a black plastic body and a chrome ring. There was a deal between Hagstrom and Guild to use them on Starfire and other basses back then (and also a marriage between the Dronge and Hagstrom family). They are single coil pickups, despite what looks like two rows of polepieces. When Rick Turner and Ron Wickersham ran tests on all the pickups they could find in the late 60s, the Bisonics were found to be the most wide range and flat frequency they could find, which was made even better when a buffer was built on the bottom of each pickup. This was one of the reasons that Starfires were chosen by Casady and Lesh back in the day. They were discontinued, I think, around 1970-71 and replaced by Guild humbuckers which were much more lackluster pickups.