Symmorium
Symmorium is an extinct genus of stethacanthid shark that lived during the Carboniferous period. Symmorium bears close similarity in size and appearance to Stethacanthus, but is missing the "spine and brush" on its back. Some paleontologists think that the two forms are simply the males and females of related species, while other scientists think they were different groups.
Symmorium sp. tooth from the Mississippian Meramecian Series of the Salem Formation, from St. Louis County, Missouri.
Symmorium elongatus from the Lower Carboniferous era (320 MYA); Serpuchov Fm..
Symmorium lamnoides from the Upper Carboniferous (295 MYA); Kasimov Fm., from Achkasovo, Russia.
Symmorium acutus and sp. from the Kazimov Formation, Achkasovo, Moscow region. Lower Carboniferous (Middle Pennsylvanian).
