This part is a Filter Lid Black with Cup Holder Lid 25702-204 10" x 11"..

 These are found on many brands of tubs like Gulf Coast Cool Nights Series, Hydro Spa, Tatum and more.. 

 Lid Top OD = 11" Wide x 10" Deep 

Lid Lip OD = 9.25"

Filter Lid, Black with Cup Holder Lid, 25702-204, 25702204,25702 204, cmp, top, cap, 11", 10", double cup, filter, filter lid cup holder, cup holder, Gulf Coast, Cool Nights Series, Hydro Spa, Tatum