In the early nineteenth century, plesiosaurs were still poorly known and their special build was not understood. No systematic distinction was made with ichthyosaurs, so the fossils of one group were sometimes combined with those of the other to obtain a more complete specimen. In 1821, a partial skeleton discovered in the collection of Colonel Thomas James Birch, was described by William Conybeare and Henry Thomas De la Beche, and recognised as representing a distinctive group. A new genus was named, "Plesiosaurus". The generic name was derived from the Greek πλήσιος, "plèsios", "closer to" and the Latinised "saurus", in the meaning of "saurian", to express that "Plesiosaurus" was in the Chain of Being more closely positioned to the Sauria, particularly the crocodile, than "Ichthyosaurus", which had the form of a more lowly fish. The name should thus be rather read as "approaching the Sauria" or "near reptile" than as "near lizard". Parts of the specimen are still present in the Oxford University Museum of Natural History.