Catalog - Globigerinita howei

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Globigerinita howei

Citation: Globigerinita howei Blow & Banner 1962

Type specimens: Plate XIV P-R; Fig. 11 (x-xiv)

Type sample (& lithostrat): sample FCRM 1645

Type age (chronostrat): Globigerapsis semi-involuta Zone, Upper Eocene

The moderately large test consists of about three whorls of faairly rapidly enlarging, inflated, slightly embracing chambers arranged in a fairly low trochospire, with about four chambers in each whorl. The equatorial profile of the test is subcircular, with a tendency to be subtriangular to subquadrate; the equatorial periphery is distinctly and broadly lobulate. In axial profile, the dorsal surface is moderately convex whilst the very inflated bulla gives a very strong convexity to the ventral surface. In axial view the primary chambers are subglobular to ovoid, the ventral surfaces of the later chambers being more strongly inflated than the dorsal surfaces; no clear dorso-peripheral shoulder is present. In dorsal view the chambers are semicircular to reniform, being of almost constant shape throughout ontogeny. The dorsal sutures are initially obscure, but they later become more distinctly and broadly depressed. The dorsal intercameral sutures are initially slightly curved, meeting the lobulate spiral suture at broad angles, but they later become subradial. The ventral intercameral sutures are subradial; they are deeply and narrowly depressed, and this depression increases towards the periphery, where the sutures are typically sharply incised, giving an almost 'bevelled' appearance to the chamber margins. The umbilicus and primary aperture are completely covered by a very broad and very strongly inflated bulla, which protrudes far beyond the ventral surfaces of the primary chambers. The bulla extends equally fair beyond the limits of the umbilicus; it is attached at or near the periphery of the first chamber of the last whorl, approximately halfway across the ventral surfaces of the succeding two chambers and at the highest point of the apertural face of the final chamber. The bulla is often approximately the same volume as the last-formed primary chamber, but may exceed it. Two or three accessory apertures are present at the margins of the bulla; two are present at the posterior part of the bulla, one over the suture between the last-formed and the penultimate chambers, and the other over the suture between the penultimate and antepenultimate chambers. On the anterior side of the bulla, a single accessory aperture may be present, situated at the suture between the bulla and the first and the first chamber of the last whorl (fig. 11, x and xia). The two accessory apertures on the posterior margin of the bulla are typically high arches, bordered by thin but distinct lips. On the anterior side of the bulla, when an accessory aperture is present, it varies from a small unlipped opening to a high, lipped arch (similar to other accessory apertures), extending, in its maximum development, along the full breadth of the first chamber of the last whorl. The primary aperture (fig. 11, xii) is a very low arch, laterally restricted to, and symmetrically arched about, the fairly small, subquadrate, deep umbilicus. Removal of the bulla discloses that the relict part of the primary aperture of the penultimate primary chamber is often visible within the umbilicus. The primary aperture may, in some cases, be furnished with a thin, more or less distinct, rim-like thickening. The wall of the primary chambers is fairly thick, and is uniformly and finely perforate; its surface is weakly cancellate and uniformly hispid. The wall of the bulla is slightly but distinctly thinner than that of the primary chambers, and it is more finely perforate and hispid.

Maximum diameter of holotype; 0.39 mm

This species is named for Professor H. V. Howe, in honour of his pioneering work in the study of the Globigerinaceae.

Remarks: As may be seen from the illustrations (Fig. 11, x-xiv), every possible morphological intermediate exists between forms which possess two accessory apertures and those with three. Some specimens possess a bulla which extends laterally to the periphery of the first primary chamber of the last whorl, and at the suture at this point there is no trace of an accessory aperture (Fig. 11, xia); these specimens are morphologically indistinguishable from the genus Globigerinita Bronmmann as restricted by Loeblich & Tappan (1957a). Other specimens of comparable size, and of otherwise identical gross morphology, from the same assemblage, possess a very small accessory aperture at the suture between the bulla and the periphery of the first chamber of the last whorl (Fig. 11, x). In yet other specimens of comparable size and form from the same assemblage, this accessory aperture is equivalent in size and shape to the others in the bulla, and these forms agree with the description of the genus Catapsydrax given by Bolli eta/. (1957); this agreement is, of course, most marked where the anterior accessory aperture is large, extending the full breadth of the first chamber of the last whorl, so that the bulla can no longer reach the periphery of that chamber and appears to be more' umbilical' in position(Fig.11,xiv). Specimens of this species are also frequent (again, even in the same assemblage) in which the bulla possesses slight but definite extensions along the intercameral sutures of the ventral surface; the accessory apertures are situated at the end of these extensions and are frequently furnished with distinct lips; these forms, although clearly conspecific with the holotype of Globigerinita howei, would appear to be referable to the taxon Tinophodella Loeblich & Tappan, 1957. As we have noted above (p. 102), the multiplicity of accessory apertures in Tinophodella ambitacrena is exceptional, for specimens of the clearly closely related Globigerinita incrusta Akers possess only three or four such apertures. The range ofvariation within G. howei thus supports our belief that the taxa Tinophodella Loeblich & Tappan, 1957, and Catapsydrax Bolli, Loeblich & Tappan, 1957, possess no valid distinctions from the prior taxon Globigerinita Bronnimann, 1951. Globigerinita howei possesses an exceptionally inflated, large and extensive bulla, which distinguishes it from all other known species of Globigerinita; however, it may, in consequence, be confused with the species described here as Globigerapsis tropicalis (see p. 124) which is distinguished primarily by its possession of a distinct change in coiling mode before the emplacement of the final adult chamber; the final chamber of Globigerapsis follows and intensifies the coiling mode demonstrated by the penultimate and antepenultimate chambers of the test, and there is no sudden change in wall structure or surface texture. Globigerinita howei differs from the other species of its genus described in this work in possessing sutures which are sharply incised into the peripherY of the last whorl.

Stratigraphical range: In the Lindi area, this species ranges from the Truncorotaloides rohri Zone Middle Eocene, to about the middle part of the Cribrohantkenina danvillensis Zone, Upper Eocene. In southern Trinidad, it has been observed by us in samples from blocks within the 'San Fernando conglomerate , which are considered here to be derived from Upper Eocene, and which form the basal beds of the Miocene (Cipero) transgression.

References:

Blow, W. H. & Banner, F. T. (1962). 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. 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

Olsson, R. K., Pearson, P. N. & Huber, B. T. (2006c). Olsson, R. K., Pearson, P. N. & Huber, B. T. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Catapsydrax, Globorotaloides, Guembelitrioides, Paragloborotalia, Parasubbotina, and Pseudoglobigerinella n. gen. In, Pearson, P. N. , Olsson, R. K. , Hemleben, C. , Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication. 41(Chap 5): 67-110. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 5): 67-110. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerinita howei Blow & Banner 1962

Globigerinita howei

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