If it's not Homarus, it's not true lobster. Rock lobster, spiny lobster, slipper lobster, Caribbean lobster—all of them are merely wannabes, riding on the fame of the authentic Maine lobster, Homarus americanus.
You can recognize members of the Homarus genus—true lobsters—by their five sets of legs, including a pair of large, meat-filled claws.
Marine scientists have identified many species of Homarus but only two of commercial importance: H. americanus, found most plentifully in the Gulf of Maine; and H. gammarus, the European lobster, found along the western European coast.
The warm-water crustaceans known as spiny or rock lobsters—found off the coast of Florida, southern California and the Caribbean—have no claws and thus no delectable claw meat. Their edible meat comes only from their tail.