Out of curiousity, what is the division you know, and where did you get it from?
Are you sure you're not mixing them up? I'm asking because I've seen people mix them up so frequently, in some cases you can even find notices in geoography books making this clear.
There's another one, too, over which I've had internet arguments before. In that one, the USA and Canada are "America", while the rest of the continent is "South America".
The given reason was: it is not called "United States of North America", it's just "America". The rest of the countries are south from there, so all that region is "South America". I don't know how extended this vision is, though (nor I know where it fits Mexico).