Catalog - Globigerina pseudobulloides

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Globigerina pseudobulloides

Citation: Globigerina pseudobulloides Plummer 1927

Type specimens: PI.VIII,figs.9a-c; 33076, Station 23

Type locality: Zone P2, Wills Point Formation, Midway Group (upper Danian), Navarro County, Texas

Type repository: Chicago; Walker Museum Collection, The Field Museum, Chicago, IL, USA

Test rotaliform, very obtusely trochoid to plane dorsally, composed of about two and one-half convolutions, of which the last consists most generally of 5 (rarely 6) highly ventricose chambers increasing rapidly in size; periphery broadly rounded and lobate; shell wall thin and distinctly punctate but finely reticulate; superior face bearing a spire of small chambers only very slightly elevated, if at all, above the circumambient chambers of the final whorl; inferior face less convex and with a very distinct, though not large, umbilical depression; aperture a single, moderately large, lunate opening on the last chamber extending from the margin to the umbilicus and edged with a narrow, delicate, flaring lip.

The general chaos existing in the literature regarding the characteristics of Globigerine forms of this type has rendered the position of this Midway species in the old synonymy rather doubtful. Careful consideration of original descriptions and those of later good authorities assign to G. bulloides d'Orbigny and G. cretacea d'Orbigny multiple apertures. As this feature characterizes other similarly constructed Globigerine forms in lower strata of the Texas section,it seems best to reserve these old names for those tests that correspond much more closely with the original definitions. Globigerina subcretacea Chapman is a very low-spired form with a general arrangement of chambers like G. pseudo-bulloides, but again the multiple openings become a diagnostic feature.

The species G. pseudo-bulloides, therefore, is especially defined by the single, finely arched aperture bearing a narrow and slightly flaring lip on the more perfect and welldeveloped specimens. From its companion form in this formation, G. triloculinoides, which presents usually 3½ chambers to the last whorl and rather conspicuously reticulate surface, this species is sharply separated by having 5 chambers and a distinctly porous but less coarsely reticulate shell surface. Most of the Cretaceous species of the Texas section that bear a general resemblance to this Midway form show multiple openings, which are considerably obscured by the mineralization of the tests in these older strata. Some forms in the lower Cretaceous formations appear to be identical with G. pseudo-bulloides of the Midway.

This species occurs commonly throughout the Midway section, but in the richly foraminiferal strata of the lower portion of the upper zone it is very abundant. Though a similar form occurs in some parts of the Del Rio formation, no confusion can possibly arise in employing this form as a marker.

Published as Globigerina pseudo-bulloides

References:

Plummer, H. J. (1927). Foraminifera of the Midway Formation in Texas. University of Texas Bulletin. 2644: 1-206. gs V O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina pseudobulloides Plummer 1927

Globigerina pseudobulloides

References:

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