Orthida

fossil lamp shell order

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Last updated

July 1, 2026

Quick Summary

The Orthida were an order of extinct brachiopods, commonly known as lamp shells. These marine organisms are particularly characteristic of Ordovician rocks, dating back approximately 505 to 438 million years ago.1

Key features of Orthida include:
* A shell composed of two parts, or valves.1
* Often, one valve is flat (brachial valve) and the other is convex (pedicle valve).1
* A radiating pattern of ribs on the shell surface.1
* Some genera, like Conchidium, are considered valuable index fossils for dating marine rocks from the Silurian Period.2

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lamp shells
Annotated classification
Order OrthidaUsually biconvex, wide-hinged, with interareas in both valves; teeth deltidiodont (leave a growth path along margin of pedicle opening); hinge structures consist of brachiophores (supporting structures), shell substance punctate or impunctate—i.e., with or without pits; more than 200 genera; Early Cambrian through Permian.Order…
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Order OrthidaUsually biconvex, wide-hinged, with interareas in both valves; teeth deltidiodont (leave a growth path along margin of pedicle opening); hinge structures consist of brachiophores (supporting structures), shell substance punctate or impunctate—i.e., with or without pits; more than 200 genera; Early Cambrian through Permian.Order…
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