oops, just found it on wikipedia, but it doesn't look as nice as the one I had. I guess the best person to ask is the lady at the bar :) she had pure lime juice right at the bottom of the glass and made it all pretty.
Also known as Rum and Coke... jigger of rum of your choice, (suggest Bacardi 8 Reserve Rum) 4 ounces Coca Cola (not, repeat not diet or anyother concoction) 1/2 cut lime rubbed on glass rim, use fresh, crystal ice...add remaining lime to garnish...
Thanks for your answers! Having looked at different sites there seems to be a debate about how to make it 'properly'. I like the version with 1/4 pure lime juice at the bottom, with lots of ice.