Carbactinoceratidae is a family of extinct cephalopods with external shells that lived around 325 million years ago, during the Carboniferous period. They were the last group of orthocones to attain sizes exceeding one meter (three feet) in length. One specimen of the carbactinoceratid species Rayonnoceras solidiforme, recently found in Arkansas, was measured at 2.5 metres (8.2 ft) long.