The banana lady from whom I buy hands of fruit at the weekend market tells me they're called "Lime Bananas" and is reluctant to say anything more. They're a sort of sick yellow-green colour outside when they're ripe, and the flesh is bright pink, acidic, and refreshing. The shape is reminiscent of Orinocos, but the flavour is completely different.
So, what am I eating? I suspect it's Monticristis, but I'd love a confirmation.