The dominant family of Ordovician Ellesmerocerida is the Ellesmeroceriatidae which are distinguished from the generally similar Protocycloceratidae by the presence of broad lateral lobes in the suture. Sutures in the Protocycloceratidae are straight and transverse. Both contain forms that are annunlate (transversally ribbed) as well as smooth. Other Ordovician families are the broad and beviconic Cyclostomiceratidae and exogastric Bassleroceratidae, rounding out the Ellesmeroceratina. Three families, the Bathmoceratidae, Cyrtocerinidae, and Eothinoceratidae differ from the others in that their connecting rings are greatly thickened inwardly as annular lobes. The Ellesmerocerida gave rise to the Endocerida through "Pachendoceras" and to the Tarphycerida and Oncocerida through "Bassleroceras" and is the source for the Orthocerida, Pseudorthocerida, Actinocerida, and Discosorida.