Actinoceratidae

Actinoceriatidae is a family of actinocerids named by Saemann in 1853 for those that grew to have large shells with blunt apecies and large siphuncles with widely expanded segments and a generally arcuate endosiphucular canal system. Their range is from the upper Middle Ordovician to the Lower Silurian. Actinocerids are generally straight shelled ...
Found on http://en.wikipedia.org/wiki/Actinoceratidae
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