It was a 14" iBook (using PowerPC processors).
Of course, the Air won't be around for too long. The same way the rMBP replaced almost completely the non-retina MBP (where a model frozen in time is kept around as a budget entry for those that want decent internal storage for a low-ish price, the 13" rMBP costs $1800 with 500 GB whereas the non-retina costs $1100), the rMB will replace the Air within a few years. Right now the Air gives you a $900 or $1000 entry point vs the $1300 for the rMB (and they come with significantly faster processor and more ports), at the cost of less RAM and storage and naturally no retina display. Once you match RAM and storage, the rMB is almost a no-brainer, except for the lower CPU power (and the one-port thing).