The Dromedary camel (Camelus dromedarius) is a large even-toed ungulate. It is often referred to as the one-humped camel, Arabian camel, or simply as the “dromedary". Its native range is unclear, but it was probably the Arabian Peninsula. The domesticated form occurs widely in northern Africa and the Middle East; the world’s only population of dromedaries exhibiting wild behaviour is an introduced feral population in Australia. The dromedary camel is arguably the best-known member of the camel family. Other members of the camel family include the llama and the alpaca in South America. The Dromedary has one hump on its back, in contrast to the Bactrian camel which has two. A good mnemonic for remembering which way around these terms apply is this: “Bactrian” begins with “B", and “Dromedary” begins with “D"; “B” on its side has two humps, whilst “D” on its side has only one hump.
Frederick Converse Beach Encyclopedia Americana (New York, NY: Americana Company, 1903)