dougp:
Datasheet states all sixteen I/O pins can detect interrupts and they can be joined to provide one signal to a controller.
You have two interrupt outputs on that chip (which in turn should trigger an interrupt on the Arduino), which tell on which group of 8 pins an interrupt occurred. After that you have to read those pins (all 8 can be read in one go) and figure out which one was triggered.
Similar to the AVRs pin change interrupts.