The tying here is for a Depth Charged Corixa, its basically a standard Plain Hackled Corixa with a large gold bead added at the thorax which allows the fly to sink very quickly. If you want the standard Corixa , the tying method is identical as below but with the gold bead removed.
Push a gold bead onto the hookshank and leave it positioned at the eye. Catch in the tying thread behind the bead. (Do not secure the bead into position just yet).