Homarus Americanus is the Latin name for lobsters from the North Atlantic. They are sometimes refered to as Maine lobsters, but not all these critters come from Maine.
American lobsters thrive in the cold waters of the Atlantic, including New England as well as Canada (so your Maine lobster may well be Canadian). Fishmongers can usually tell you where your lobster’s from, but the news is that lobsters from Maine will soon wear tags to make them easily identified.
Here’s some interesting reading on the topic.
Board Links: Lobster tag–certifiably in Maine?