This a very lightly used Zen Underwater DP-100 S4 100mm Glass Fisheye Port for Subal housings with Type 4 port mount. The glass is very clean, with very minor marks on the dome shade. The port also comes with a Subal 15mm Extension Ring, Xit 404 Subal Type 4 Rear Port cap and a vinyl front port cover. Selling price $750 plus shipping.
I also have two Subal Type 4 extension rings, one is a 50mm, and the other is a 40mm for sale.
You can take both for $200 USD, or individually for $125 each.