MORPHOLOGICAL REASSESSMENT OF SOME ZONATE AND CORONATE MEGASPORE GENERA OF MAINLY POSTPALEOZOIC AGE

An analysis of Mesozoic and Tertiary megaspore assemblages from NW Eur ope has shown that several zonate and coronate genera are not adequate ly differentiated on the basis of their original diagnoses. A number o f the species that have been described previously, and a few new forms recently encountered, display characters that are attributable to mor e than one genus. The genera considered are Auriculizonospora, Capilli sporites, Dijkstraisporites, Flabellisporites, Henrisporites, Herbosis porites, Membranisporites, Minerisporites, Pavlovisporites (a monotypi c Permian form), Paxillitriletes, Sepisporites, Tenellisporites and Tr iangulatisporites. A comparison of the morphology of all of the specie s within this group that are known to us has enabled a reassessment of the criteria on which they can be distinguished. As a result (1) Auri culizonospora is reinstated as a genus that is distinct from Minerispo rites, (2) the diagnoses of these two genera, Dijkstraisporites, Paxil litriletes and Tenellisporites are emended, (3) Membranisporites is pl aced in synonymy with Paxillitriletes, (4) six species are newly combi ned with other genera, and (5) one is renamed. The nomenclatural chang es are as follows: Dykstraisporites (al. Minerisporites) pterotus (Sin gh, 1983) comb. nov., ?Flabellisporites (al. Tenellisporites) spinatus (Peake, 1968) comb. nov., Minerisporites archangvillarae nom. nov. (n ew name for Minerisporites elegans Archangelsky and Villar de Seoane, 1989, a junior homonym of M. elegans Li Wenben and Batten, 1987), Mine risporites (al. Henrisporites) levis (Lachkar, 1979) comb. nov., Miner isporites (al. Dijkstraisporites) psilites (Gunther and Hills, 1972) c omb. nov., Paxilitriletes (al. Triletes) ales (Harris, 1935) comb. nov ., and Paxillitriletes (al. Triletes) samarus (Dijkstra, 1951) comb. n ov. Although a few forms remain difficult to place because of their '' intermediate'' character, it is now possible to refer the majority to genera with greater confidence than hitherto. The chances of both taxo nomic and nomenclatural confusion, and of biostratigraphic misinterpre tation should, therefore, be reduced in the future. Most of the genera are thought to have isoetalean origins but the three Triassic species that have been referred to Triangulatisporites, and some of the other species from this geological period may well be selaginellalean spore s.