Identification key for North American Ordovician trepostome families

Many paleontologie studies depend critically upon species-level data, and bryozoan paleo- ecologic, reefal, biostratigraphic and evolutionary investigations are no exception. A consistent and useable taxonomic framework is essential for understanding the similarities and relationships among those species. Experiences with North American Ordovician bryozoans suggest that the lowest (genus down) and highest (suborder up) taxa as recently modified are adequate, but that – for trepostomes -- intermediate-level ones (families) in the present literature are difficult to diagnose, recognize, and apply. However, several morphologic characters can be used to construct a pragmatically useable identification key for 15 such trepostome families. Colony size and form, branch thickness, exozonal wall thickness, wall microstructure, zooecial diametre, meso zooecia abundance and appearance, acantho style abundance and size, cystiphragms, curved diaphragms, straight diaphragms, and hemiphragms all contribute to this taxonomic improvement.