And you thought Centaurs didn't exist...

Although as a female, technically she would be one of the Kentaurides:

"How beautiful the Centaurides are, even where they are horses; for some grow out of white mares, others are attached to chestnut mares, and the coat’s of others are dappled, but they glisten like those of horses that are well cared for. There is also a white female Centaur that grows out of a black mare, and the very opposition of the colours helps to produce the united beauty of the whole."

I guess the one above is the white female growing out of a black mare.