hoop snake

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun In folklore, a kind of snake that grasps its tail in its mouth and moves with a rolling, hooplike motion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A mythical creature of the United States and Australia, a snake that grasps its tail in its jaws and thereby rolls after its prey like a wheel.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various harmless North American snakes that were formerly believed to take tail in mouth and roll along like a hoop