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Messinian (Uppermost Miocene) outcrops near the town of Oran in western Algeria yielded rich bryozoan faunas: 188 species and forms. Bryozoans were studied in ten different deposits and 27 horizons representing various marly and calcareous facies. The number of species is lowest in the coral reefs (51), intermediate in the coralline‐algae limestones (95), and highest in the mark(167). Also, zoarial growth forms are more diverse in marly deposits than in calcareous ones. These differences are interpreted in terms of bottom substrate, depth, deposition rate, and hydrodynamic conditions. An analysis based on zoarial growth forms and known bathymetric ranges of species still living gives more precise depth indications for each studied assemblage. A detailed survey of these assemblages in several sections shows that a gradual lowering of regional sea level occurred during the Messinian. From the presence of a …