Black & Tan Redux
Serves me right for not Googling "Black & Tan" before I actually made the entry.
According to this site, the irish don't consider a Black & Tan a Black and Tan if it has Bass Pale Ale in it. Apparently, Bass is not readily available in Ireland. However, Since Harp Lager is produced by the same brewery, the most common version of a Black & Tan is half Harp, half Guiness.
Go to this page to start for all things Guiness. There's even a song for Black & Tans. Or check out Guiness' web site at guinness.com for more information.