This is a simple enough pattern,I use devcon 5 minute epoxy,just mix the two tubes,a pea sized amount is ideal.the added weight of the epoxy gives it a nice action.
Materials:-
kamasan B170 12-16
UTC thread 140 - brown/tan
silver tinsel
cock pheasant tail for shellback
brown rubber legs

Attach thread and run down shank tying in 8-10 pheasant tail fibres,then run thread back towards eye.

Tie in tinsel,even turns down to shellback and back again,tie off at eye.

Tie in 1 strand of the rubber legs,figure of eight.

Bring PT over the top and secure at eye.I trim the legs to same length as rear of hook shank.,give them a touch of black permanent pen on the tips ,as the corixa's paddles are black on the ends.

Mix the epoxy and,using a dubbing needle put a 'blob' on the underside of hook.

Part rotate hook in vice for a minute or so to give an even shape to the underside of the fly,then leave to dry.

The finished fly should have a nice bulbous silvery transparent look as though it's the air bubble trapped by the corixa as it makes its way back down from the surface.