Catalog - Polyperibola christiani

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Polyperibola christiani

Citation: Polyperibola christiani Liska 1980

Type sample (& lithostrat): Brown, calcareous claystones, Type sample: T.C.283/R.D.L.319.

Type age (chronostrat): Globorotalia acostaensis Zone of the late Miocene.

Type locality: south side of the Lizard Road, between Rio Claro and Guayaguayare at coordinates N. 191625 links, E.553063 links.; Trinidad

Type repository: Washington; USNM, additional specimens in NHM London and NHM Basel.

Test small to medium sized, subcircular, lobulate in any view, initially trochoid, generally sinistral with two whorls of five and four chambers respectively (excluding final chamber); chambers globular, loosely appressed; a large final chamber develops over umbilical area; supplementary chambers and bullae hemispherical and irregularly shaped, cover much of suture of final chamber, and develop onto early portion of test over intercameral sutures of trochoid whorls; all sutures of trochoid whorls straight to slightly curved and incised; sutures of supplemental chambers and bullae distinct; increase in chamber size per trochoid whorl small, diameter increase of second to first whorl is 2:1; no visible primary aperture; as final chamber, supplementary chambers, or bullae develop over earlier portions of test, they contain multiple, semicircular, sutural, apertures with imperforate rims; test radial calcite; chamber walls thin, fragile, finely perforate, and appear vitreous; small pustules develop on the chambers of the trochoid whorls; increase in number and are concentrated along intercameral sutures, appear to increase in aerial extent on older chambers; supplementary chambers with few pustules, thinner walled, more vitreous, and are finely perforate.

after Mr. James T. Christian, colleague and discoverer of the type locality.

Remarks. The variation in Polyperibola christiani is extreme, and from a syntipic series of 230 specimens no two could be said to be identical. The selection of the holotype is based on a specimen which best represents the unit characters of the species. The size, shape and number of the supplementary chambers and bullae differ considerably between specimens, as shown by the forms illustrated in Pls. 1-3. Although both dextral and sinistral forms occur, the trochoid portion of the test generally coils to the left. The distinction between the term “supplementary chamber” and the term “bulla” is based solely on size, not shape nor location on the test. Both are included in the measurement of maximum test diameter which ranges from 0.173 to 0.407 mm. Some forms are so completely enveloped by supplementary chambers and bullae that the initial trochoidal growth stage is not visible, giving the test a botryoidal appearance.
The number of chambers per whorl in the trochoid portion of the test is not constant, and two or, rarely, three whorls may be present. The trochoid chambers increase very little in size within a whorl, and each whorl is approximately twice the diameter of the previous whorl. In broken forms the ultimate chamber, rarely the penultimate, covers a slit-like or multiple-slit primary aperture. All chambers developed subsequent to the trochoid whorl are considered to be supplementary, and only the supplementary chambers and bullae contain the distinctive, rimmed, multiple apertures.

References:

Liska, R. D. (1980). Polyperibola, a new planktonic foraminiferal genus from the late Miocene of Trinidad and Tobago. Journal of Foraminiferal Research. 10(2): 136-142. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Polyperibola christiani Liska 1980

Polyperibola christiani

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