[nominatronic]

It's a transformer - I'm guessing it's the magnetics for the 10base2 port.

You can see the two pairs of enamel wires coming out on each side the sides. There are two windings, both wound on a core spool with its axis perpendicular to the board.

What you're seeing looking like the lens of a camera is a hole in the middle of the spool, presumably used during manufacture to hold it while winding.