First thing first. What is "A Free Species"? I mean, there's obviously animals out there living freely in the wild and what-not, right? Right. And thier free, right? Well...yes and no. Let me explain.
The animals out in the wild are, indeed, free...but to a certain extent. They can be caught and thrown into captivity just as easily as a frog near a child's backyard pond, and there is no law saying that people can't do this. The Free Species are animals who have rites. Animals who cannot just be thrown into a cage and whisked off to some lonely, rich man looking for company. The Free Species are animals who are extremly intelligent and/or powerful, ones who can choose whether they want to be stuck in captivity or no.
Most commonly, The Free Species are Dragons and Pheonixes, the two most powerful sorts of beings in all of Nonus(or so it is said). The Free Species is also any animal that can speak one, or more, or the main four Lomeelian languages. These are also the best sort of familiars, for they get to choose who to be a familiar two.