Catalog - Pseudohastigerina barbadoensis

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Pseudohastigerina barbadoensis

Citation: Pseudohastigerina barbadoensis Blow 1969

Type age (chronostrat): Oligocene, Zone P. 19 Globigerina sellii Pseudohastigerina barbadoensis Concurrent-range zone, Cipero Formation. Ranges from Zone P. 16 (Upper Eocene) to the top of Zone P. 19 (Oligocene).

Type locality: From the lowest part of the Cipero Formation (sample Cb.1 964), north San Fernando, Trinidad, West Indies.

The small test is composed of about 17 chambers coiled in an evolute planispire with 7 ½ chambers visible in the final whorl. The test is moderately laterally compressed but the periphery is gently rounded. The chambers of the last whorl are slightly inflated and the intercameral sutures only shallowly depressed; the intercameral sutures between the last few chambers of the final whorl show a banded appearance due to a greater degree of smoothness of the wall and to a reduction in the density of the pores. In some parts of the intercameral sutures, pores seem to be virtually absent or very fine. In optical appearance the test seems to be finely perforate but stereoscan electron-microscopy shows comparatively large pores moderately densely scattered over the test surface. The pores seem to open to the exterior without any distinct pore-pits. The evolute test possesses a wide umbilicus and the relict apertures of the last two chambers can be seen. The apertural porticus is well developed and the junction of the porticus and the test wall in the apertural region forms a virtual right angle. The aperture is a moderately low arch and is completely bordered by the porticus which seems to be imperforate. The wall is calcareous, radial hyaline and slightly pustulose but the surface is without distinct pore-pits.

Maximum diameter of holotype 0.2mm.

Remarks. - This species is distinguished from Pseudohastigerina micra (Cole) [Nonion micrus, 1927] by the banded appearance of the intercameral sutures of some, at least, of the chambers of the final whorl. The degree of inflation of the chambers is similar to those of P. micra but the sutures are not so deeply incised in P. barbadoensis. Usually, P. barbadoensis is considerably snnaller (for a given ontogenetic stage) than P. micra and the more evolute coiling in P. barbacloensis forms a further taxonomic distinction. P. barbadoensis differs from P. naguewichiensis (Myatliuk) [Globigerinella naguewichiensis, 1950] in the rather more rapidly opening coil, and in having less inflated and less hispid chambers. In P naguewichiensis the chambers are subglobular and inflated with quite strongly depressed and incised sutures. In some rarely occuring specimens of P barbadoensis the periphery becomes somewhat ridged and subacute in apertural peripheral view; these forms have, so far, only been noted in the later part of Zone P .19 [= Sphaeroidinella dehiscens dehiscens Globoquadrina altispira altispira Partial-range zone] . When the surface of P. barbadoensis has been eroded, a somewhat pitted appearance obtains but this is not present in unaltered specimens which have no natural pore-pits.

References:

Blow, W. H. (1969). Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In, Bronnimann, P. & Renz, H. H. (eds) Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967. E J Brill, Leiden 380-381. gs

Olsson, R. K. & Hemleben, C. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene Globanomalina, Planoglobanomalina n. gen and Pseudohastigerina. 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 14): 413-432. gs O

Pearson, P. N., Olsson, R. K., Spezzaferri, S. & Leckie, R. M. (2018a). Taxonomy, biostratigraphy, and phylogeny of Oligocene Globanomalinidae (Turborotalia and Pseudohastigerina). 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 14): 403-414. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Pseudohastigerina barbadoensis Blow 1969

Pseudohastigerina barbadoensis

References:

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