Cleiothyris Phillips, 1841, Mikrothyris Atrypa is a genus of brachiopod with round to short egg-shaped shells covered with many fine radial ridges (or costae).

Atrypa had a large geographic range and occurred from the late Lower Silurian (Telychian) to the early Upper Devonian (Frasnian).

[4] Other sources expand the range from the Late Ordovician to Carboniferous, approximately from 449 to 336 Ma.

[3] A proposed new species, A. harrisi, was found in the trilobite-rich Floresta Formation in Boyacá, Colombia.

However, only the more stable amino acids tend to be preserved in older Atrypa fossils.