This is apparently one of the very few Greyhound motorcycles left in existence. It would appear to be a 1911-12 model.
The name E.R Thomas was associated with several motor-related ventures in Buffalo around the turn of the century. Among them are The Auto-Bi Company, Buffalo 1907-1909, Greyhound Motor Works, Buffalo 1909-1910, Greyhound Motor Company, Buffalo 1911-1912. None appear to have been any great commercial success. History here. Start about page 154.