The samples were prepared from unprocessed material as smear slides and were examined under a light microscope at 1250x magnification. First, all samples were examined with qualitative methods. Successively, the presence or absence of index species in the stratigraphic intervals critical for detecting the various biohorizons were checked by using the quantitative and semiquantitative counting methods suggested by Thierstein et al. (1977), Backman and Shackleton (1983), Rio, Fornaciari, et al. (1990), and Rio, Raffi, et al. (1990). Semiquantitative data have been collected by counting the index species in 1-mm2 squares (i.e., Amaurolithus, Ceratolithus, Sphenolithus, Gephyrocapsa, and Pseudoemiliania lacunosa). The quantitative data have been collected by counting the index species relative to a prefixed number of taxonomically related forms (species of helicoliths relative to 10-50 helicoliths; Reticulofenestra pseudoumbilicus, Cyclicargolithus floridanus, and P. lacunosa relative to 50-100 reticulofenestrids; species of Calcidiscus relative to 10-50 Calcidiscus; Coccolithus miopelagicus relative to 10-100 Coccolithus; species of Discoaster relative to 30-200 discoasterids; and species of Gephyrocapsa relative to 100-300 Gephyrocapsa).
The considered taxa are reported in alphabetic order and by generic epithets in Appendix A. Bibliographic references for the species are given in Loeblich and Tappan (1966, 1968, 1969, 1970a, 1970b, 1971, 1973), Aubry (1984, 1988, 1989, 1990), and Perch-Nielsen (1985). The adopted taxonomic concepts are those of Rio, Fornaciari, et al. (1990); Rio, Raffi, et al. (1990); Fornaciari et al. (1990); and Raffi et al. (1993) and are summarized in the taxonomic notes.