rock crab

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

• noun Any of various crabs found along rocky coasts, especially one of the genus Cancer, having a broad, usually oval carapace.

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

• noun Hemigrapsus sexdentatus, a large-eyed marine crab found off the coast of New Zealand
• noun Cancer irroratus, a crab with large marginal teeth found along the Atlantic coast of North America

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

• noun crab of eastern coast of North America