What is one of an extinct genus of fossil cephalopods, allied to the Ammonites. The earliest forms are found in the Devonian formation, the latest, in the Triassic called?

goniatite — One of an extinct genus of fossil cephalopods, allied to the Ammonites. The earliest forms are found in the Devonian formation, the latest, in the Triassic. (Webster's 1913.)

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