In the Ecardines, of which Lingula and Discina may be quoted as examples, the myology is much more complicated.
Undue stress is often laid on the fact that Lingula has come down to us apparently unchanged since Cambrian times, whilst Crania, and forms very closely resembling Discina and Rhynchonella, are found from the Ordovician strata onwards.
Other common genera are Spirifer, Chonetes, Athyris, Rhynchonellids and Terebratulids, Discina and Crania.
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