A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species which have been described previously, or are related. The species description often contains photographs or other illustrations of the type material and states in which museums it been deposited. The publication in which the species is described gives the new species a formal scientific name. Today, some 1.9 million species have been described and named, out of some 8.7 million that may actually exist on Earth. Millions more have become extinct.