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Species Globorotalia tortiva Bolli 1957


Diagnosis / Definition:
Bolli (1957):
Shape of test very low trochospiral, spiral side almost flat, umbilical side strongly convex; equatorial periphery lobate, chambers give a quadrangular to pentagonal outline; axial periphery rounded to subangular. Wall calcareous, perforate, surface finely spinose. Chambers laterally strongly compressed; 10-12, arranged in 2-2 1/2 whorls, the 4-4 1/2 chambers of the last whorl increasing rapidly in size. Sutures on spiral side curved in early chambers, often straight, oblique between penultimate and ultimate chambers, depressed; on umbilical side radial or slightly curved, depressed. Umbilicus narrow, open. Aperture a high arch; interiomarginal, extraumbilical umbilical. Coiling 85 percent dextral in the only sample investigated. Largest diameter of holotype 0.33 min.
Discussion / Comments:
Bolli (1957):
White (1928) described an identical form from Mexico under the name Globigerina velascoensis var. compressa. The interiomarginal, extraumbilical umbilical position of the aperture places it within the genus Globorotalia where it becomes a homonym of G. compressa (Plummer). For this reason the new name G. tortiva is proposed. G. tortiva possibly branched off from Globigerina velascoensis which has less compressed chambers and an umbilical position of the apertures.
Systematics:

20
 Genus Globorotalia
  Species Globorotalia tortiva
Synonym list:
Bolli (1957):
1928 Globigerina velascoensis var. compressa White. - White : p. 196 pl. 28, figs. 3a-b
1957 Globorotalia tortiva Bolli. - Bolli : pl. 19, figs. 19-21 new subspecies
References:

White,M.P. (1928):
Some index foraminifera of the Tampico embayment of Mexico, Part 2 . Journal of Paleontology Vol. 2(4) p. 280-313

Bolli,H.M. (1957):
The genera Globigerina and Globorotalia in the Paleocene-Lower Eocene Lizard Springs Formation of Trinidad, B.W.I . Bulletin of the U.S. National Museum Vol. 215 p. 61-82
Anonymous: Unedited TaxonConcept data
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