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Rhynchotrema
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Ordovician Period
lamp shells
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Rhynchotrema

fossil brachiopod genus
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Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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Rhynchotrema, extinct genus of brachiopods, or lamp shells, found as fossils in Middle and Late Ordovician rocks (the Ordovician Period lasted from 505 to 438 million years ago). The shell is small and distinctive for its strongly developed ribbing. Rhynchotrema is a useful Ordovician index, or guide, fossil.