Which Airport Card do I need?

I bought this Powerbook G4 12 inch running OSX 10.4.11 from eBay. The seller said it had WiFi - it doesn't the Airport card slot (under battery) is empty. I am unsure which Airport card I should buy.

I have already been ripped off (again) via eBay with a USB wireless adapter that claimed to work with OSX but it later transpired only worked with 10.5 onward.

Any advice would be greatfully received.

Thank you.