This is the Air Injection Belt that is attached to the water pump.  For models for California, Australia, & Japan 1966-1980  Silver Shadow, Shadow II, T-2, Silver Wraith II 1980-1998...

This is a pair of belts that run between the water pump and crank pulley. 1968 from VIN 11111 onward 1980-1986 VIN 01001-16970        

This is a pair of belts that run between the steering pump and the air conditioning compressor. 1966-1980 All Models and VINs 1980-1989 all Models up to VIN 27780