I'm browsing eBay for my own entertainment. This stone looks strikingly like an August Vintage Cushion, to me:
http://www.ebay.com/itm/ESTATE-1900-ANTIQUE-ART-DECO-CUSHION-CUT-1-20CT-DIAMOND-TAPERED-BAGUETTE-RING-/370642803696?pt=US_Fine_Rings&hash=item564c085bf0

http://www.ebay.com/itm/ESTATE-1900-ANTIQUE-ART-DECO-CUSHION-CUT-1-20CT-DIAMOND-TAPERED-BAGUETTE-RING-/370642803696?pt=US_Fine_Rings&hash=item564c085bf0
