The Mayfly Halo Emerger is explained and described here.
When you tie it, you’ll have to start at the rear. Wrap the Antron or Z-lon from about the barb, a bit down the curve and the back again. Secure with thread and tie in 2-3 tips of a Ostrich Mini Plumes (originally Marabou). I prefer to use two.
Then go back up to about 1/3 of the shank length from the hook eye. Wind the thread in a figure-eight motion, binding a strip of foam (the type you’ll find electrical articles are wrapped in when new) onto the shank. Fold the strip back on each side and tie two loops of foam. Secure with figure eights. Then dub abdomen, slightly tapered towards the thorax. Tie in a spike of fiery orange deer hair.
Even if the fly looks strange, it works fantastic as a general mayfly emerger. Vary the colors of the abdomen to suit your waters and the hatches you’d like to imitate.