Orthoceras

Orthoceras, a, genus of Nautiloidea (q.v.), which includes long, straight-chambered shells which are often of great length. The genus ranges from the Upper Cambrian beds to the Trias of the Alps. It is, however, mainly characteristic of the lower part of the Palaeozoic group. It is the type of the family Orthoceratidce. Some 'large species in China are cut open and polished and then used as religious symbols; they have been described by travellers as "Pagoda shells."