TAXONOMIC NOTES

Reticulofenestra spp. Species within this genus are generally distinguished on the basis of the overall size of the shields, the size of the central opening, and the width of the wall. Considerable confusion nevertheless exists in the taxonomy of the genus, with exact species concepts differing among authors. We shall not attempt to review here the often conflicting literature. The interested reader is referred to Backman (1980), Pujos (1985), Gallagher (1989), and Young (1990) for some of the more detailed examinations of this plexus. The following reticulofenestrid concepts are used in this study:

R. rotaria. A rare but distinctive circular form found in the late Miocene.

R. pseudoumbilicus. An elliptical form with a long dimension of at least 7 µm.

R. gelida. A form that is also 7 µm, but with a distinctly smaller central area than R. pseudoumbilicus. Gallagher (1989) considered this form to be a junior synonym of R. pseudoumbilicus.

R. minuta. Forms <3 µm in length.

R. minutula. Forms 3-6 µm in length. Some authors describe this species as ranging up to only 5 µm in length, but this concept would leave us with the problem of what to do with the occasional 6-µm reticulofenestrid. In the literature, these 6-µm forms are often assigned to R. pseudoumbilicus (e.g., Backman, 1980). Because the 7-µm R. pseudoumbilicus designation seems to have biostratigraphic value (Rio et al., 1990a; Young, 1990), whereas the 6-µm forms do not, we also assigned the 6-µm forms to R. minutula s.l. in (Table 2, Table 3, Table 4, Table 5, Table 6, Table 7).

R. haqii. This form has the same length as R. minutula s.s. (3-5 µm). The difference between the two is the size of the central opening. R. minutula has a central opening >1.5 µm, whereas R. haqii has an opening <1.5 µm (Backman, 1980). We found this distinction difficult to apply consistently, and of no apparent biostratigraphic value. Pujos (1987) considered the two forms to be ecotypes of the same species; Gallagher (1989) also believed them to be synonymous. R. minutula is the senior synonym and is used here.

Crenalithus (or Reticulofenestra) doronicoides. This form has been discussed by numerous authors, with various interpretations as to the validity of the name, its taxonomic position, common usage, relationship to other species, and stratigraphic range (e.g., Backman, 1980; Matsuoka and Okada, 1989; Young, 1990). Backman (1980) considered the type specimens of Crenalithus (or Reticulofenestra) doronicoides to have exactly the same morphology as R. minutula. One does get the impression from some range charts that R. minutula is rather arbitrarily used in the Miocene and lower Pliocene and C.(R.) doronicoides in the upper Pliocene and Pleistocene for very similar specimens. In any case, Backman (1980) rejected the name "doronicoides" on the grounds that it could not be distinguished from one or more other legitimate species. Moreover, Young (1990) examined topotypic material which cast doubt on the very validity of the epithet "doronicoides"; he rejected it, considering it to be a junior synonym of Gephyrocapsa oceanica (forms of G. oceanica that have lost their bridges). We thus use R. minutula s.l. instead of "C.(R.) doronicoides" for these forms on our range charts.

Pseudoemiliania lacunosa. The validity of this species has received at least as much discussion in the literature as C. (R.) doronicoides. Matsuoka and Okada (1989) and Young (1990) provided useful reviews which we shall not repeat here. Although we have not followed Young's (1990) change of Pseudoemiliania to Reticulofenestra, we do agree with Young (1990) and others that P. lacunosa has two distinct varieties: an elliptical form and a circular form. We have indicated the varieties simply as P. lacunosa E (= elliptical) and P. lacunosa C (= circular) on our range charts.

Scyphosphaera. This genus comprises a large number of species (53 have been named), many based on only the slightest morphological differences. The most frequently encountered species in Leg 161 holes, and elsewhere, is S. apsteinii. The forms that have been named S. biarritzensis Lezaud, S. brevis Varol, and S. procera Kamptner are very similar in shape to S. apsteinii, and may merely represent intraspecific variation. We have, nevertheless, continued to list "squat" forms resembling S. apsteinii s.l. as S. brevis, and "slim" forms as S. procera on the range charts. Several specimens resembling S. aranta Kamptner and S. oremesa Kamptner were seen, but close examination showed that the lobate/domed margins (diagnostic for the definition of the species) are the result of breaking away parts of the lower margin. Siesser and Bralower (1992) reported rare specimens of these two species in Hole 762B (Exmouth Plateau). Re-examination of those specimens also shows their shape to be the result of breakage. Indeed, S. oremesa has never been validly reported in the literature since its erection by Kamptner (1967), and the few reports of S. aranta have not been confirmed.

NEXT