The link that Cheetah so nicely provided told me that the one I was referring to is the Ataulfo variety. They're more expensive than the others, and are rarely available out of season. :-)

I wish I was closer to the tropics for fruit - I know that many of these things are delicate and don't survive long-distance travel. One day, I'll have to travel - but to the warmer countries instead of always to the colder ones!