Eighty-seven genera of small minnow mayflies (Ephemeroptera: Baetidae) are currently known from throughout the world. Thirty-seven genera occur in the Afrotropics, 27 in the Neotropics, 21 in the Nearctic, 21 in the Oriental region, 14 in the Palearctic, and nine in the Australian region (including Papua-New Guinea). The Afrotropics currently have 84% endemic genera, the Neotropics 63%, Australia 44%, the Orient 43%, and the Nearctic and Palearctic have considerably less due to their close relationship. Coefficients of similarity among the biogeographic regions indicate that the Holarctic (Nearctic + Palearctic) and Oriental regions are most similar in generic composition. The Afrotropics demonstrate considerable insular evolution, but widespread Holarctic and Oriental genera are also found there. The Neotropics demonstrate the highest degree of insular evolution, and although South America essentially has not been colonized by genera from outside its region, certain Neotropical lineages have infiltrated the Nearctic in more recent geologic history. Australia remains poorly documented, but available data suggest that it has been considerably influenced by dispersal from the Oriental region. Problems and prospects for the further study of the global biodiversity of baetids are discussed. Baetids from the now poorly known areas of western Africa, Australia and India in general, and northeastern South America may significantly add to an overview of diversity and biogeography of the family.

¹Purdue ARP Journal No. 15997