Indiana University-Purdue University Indianapolis (IUPUI) / Two closely related families of Ordovician bryozoans, the Monticuliporidae and the Mesotrypidae, collectively contain 12 genera that have been reclassified repeatedly by various authors. Using published illustrations for the type specimens of each genus, character states for 267 morphological attributes were coded. Cladistic results were compared between the programs PAST and PAUP, and contrasted with phenetic methods. PAUP produced the shortest trees, with better summary index values and low homoplasy. Phenetic results varied, depending largely on the similarity measures used. Cladistic analysis produced five tree topologies, the most parsimonious of which consisted of a monophyletic crown group, representing Family Monticuliporidae, and a paraphyletic stem group that included the genera Mesotrypa and Diazipora. The crown group includes the genera Aspidopora, Atactoporella, Acantholaminatus, Peronopora, Homotrypella, Homotrypa, Gortanipora, Monticulipora, Prasopora, and Prasoporina. The paraphyletic stem group matches Astrova’s concept of Family Mesotrypidae. These results suggest the placement of all 12 genera in a single Family Monticuliporidae. Future studies that include data for additional closely related genera in might provide a clearer picture of familial assignments for these, and other, stenolaemate genera.