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The large test consists of about three whorls of rapidly enlarging, moderately inflated, partially embracing chambers coiled in a low trochospire. Four chambers are typically present in the early whorls characteristically reducing to three in the last whorl. The equatorial profile of the test is subcircular to subquadrate and the equatorial periphery is weakly and broadly lobulate. In axial profile the test is subconical; the dorsal surface is only slightly convex, whereas the ventral side is strongly vaulted. The axial periphery is broadly and smoothly rounded, but there is a distinct, although broad, dorsa-peripheral shoulder.
Dorsally, the sutures are initially obscure but they become more distinctly depressed during ontogeny; the dorsal mtercameral sutures are initially curved, meeting the moderately lobulate spiral suture at broad angles, but between the last two chambers the suture.may become subradial. In ventral view only three chambers are visible· the last chamber is of distinctly reniform shape,' whilst the earlier two chambers are subreniform and the suture between them is subradial and deeply depressed. In dorsal view the early chambers are semicircular but they become reniform, depressed, and longer than broad during ontogeny. The dorsal surfaces of the chambers are of uniform and gentle convexity throughout ontogeny.
The umbilicus is small and is often almost completely covered by the last formed chamber. The umbilicus is typically of triangular shape, but this may vary; it is open and deep but is not usually sharply delimited. The apertural face is a fairly broad, flattened, reniform re-entrant in the ventral face of the last chamber; it is often distinctly less hispid than the remainder of the chamber wall.
The aperture extends the width of the umbilicus, along the length of the re-entrant in the ventral face of the last chamber; it is often less hispid than the remainder of the chamber wall. The aperture may vary from a very low to a moderately high arch, but it is always clearly restricted laterally to the reentrant of the apertural face, which is frequently bounded by lateral lobe-like expansions of the ventral surface of the last chamber. The aperture is furnished with a lip which sometimes is merely rimlike, but which may broaden medially to form a weak 'umbilical tooth'.
The wall of the test is fairly thick, moderately coarsely perforate and uniformly and strongly hispid.
Size: Maximum diameter of holotype: 0.65 mm;
Extra details from original publication
Remarks: In any observed population of Globigerina oligocaenica there exists slight but noteworthy variation in the rate of enlargement of the later chambers this affects the over-all shape of the test in so far that some specimens may be more globose whilst others may be more quadrate than the holotype. In consequence, there is a comparable degree of variation in the breadth of the later chambers as seen in dorsal view and a similar variation in the degree of overlap of the ventral side of the last chamber over the umbilicus and early chambers of the last whorl. The hispidity and pore size are reduced on the apertural face of some specimens, and this reduction also occurs on the septa.
Globigerina oligocaenica differs from G. tripartita tripartita in having more rapidly enlarging chambers which are much more strongly hispid, and in possessing an aperture which is distinctly limited in lateral extent to a well marked re-entrant in the apertural face.
Globigerina oligocaenica differs from G. tripartita tapuriensis in possessing more strongly depressed chambers, a less lobulate periphery, a more flattened dorsal surface, a smaller umbilicus, a more restricted intraumbilical aperture set at the base of a distinctly flattened apertural face, and in possessing a much more strongly hispid test (see p. 146).
Stratigraphical range: This species has only been observed in beds containing Nummulites intermedius-fichteli and N. vascus in the Lindi area, which are considered to be Lattorfian- Rupelian (Lower to Middle Oligocene). It has not been observed in numerous Upper Eocene samples from either the East African or Caribbean regions. It does not occur in the Globigerina ampliapertura Zone, Cipero formation (lowest Aquitanian) and has not been seen in any lowest Aquitanian sample from the Mediterranean or in any sample from the Vicksburgian and Jacksonian of the American Gulf States. A transitional form between G. tripartita tapuriensis and G. oligocaenica has been observed in a sample from the Lower Oligocene of Sarawak (seep. 71). The occurrence of this species is reported to us by Bolli and Bermudez (privately, see p. 71) from the Dominican Republic and Cuba, in beds which should be considered to be of pre-ampliapertura Zone age. We have seen and confirmed their specimens of this species from the lower Alazan formation of Mexico, which indicates that the lower part of this formation is of Oligocene age.
[Blow and Banner, 1962, op. cit., p. 146] : "Postscript. - Whilst in page proof we received a copy of Dr. Borsetti's paper (1 959, Ann. Mus. Geol. Bologna, Giorn. Geol., ser. 2, vol. 27, pp. 205-212). The kind loan of topotypes and paratypes indicates that, throughout our work above, ... G. oligocaenica should be referred to as C. sellii (Borsetti) [Catapsydrax sellii, 1959]. The occurrence [of G. sellii] , however, in the Lower Oligocene of North Italy, is in accord with and confirms our stratigraphical associations."
Blow, W. H. & Banner, F. T. (1962). The mid-Tertiary (Upper Eocene to Aquitanian) Globigerinaceae. In, Eames, F. E., Banner, F. T., Blow, W. H. & Clarke, W. J. (eds) Fundamentals of mid-Tertiary Stratigraphical Correlation. Cambridge University Press, Cambridge 61-151. gs Wade, B. S., Pearson, P. N., Olsson, R. K., Fraass, A. J., Leckie, R. M. & Hemleben, C. (2018c). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Dentoglobigerina and Globoquadrina. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 11): 331-384. gs V O
Blow, W. H. & Banner, F. T. (1962). The mid-Tertiary (Upper Eocene to Aquitanian) Globigerinaceae. In, Eames, F. E., Banner, F. T., Blow, W. H. & Clarke, W. J. (eds) Fundamentals of mid-Tertiary Stratigraphical Correlation. Cambridge University Press, Cambridge 61-151. gs
Wade, B. S., Pearson, P. N., Olsson, R. K., Fraass, A. J., Leckie, R. M. & Hemleben, C. (2018c). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Dentoglobigerina and Globoquadrina. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 46(Chap 11): 331-384. gs V O
Globigerina oligocaenica compiled by the pforams@mikrotax project team viewed: 23-7-2021
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