Catalog - Pulleniatina obliquiloculata praecursor

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Pulleniatina obliquiloculata praecursor

Citation: Pulleniatina obliquiloculata praecursor Banner & Blow 1967

Type age (chronostrat): High horizon of Zone N. 19 (early Pliocene).

Type locality: Stainforth sample 19305, from Ecuador, Unit 59 of Cushman and Stainforth ( 1951, pp. 130- 13 1, 142); Borb6n Formation ("Punta Gorda"), on the north coast, between Rio Chevele and Estero Cienago (Campo Allegre), 345 km. north and 13 km. east of the Plaza del Centenario monument in Guayaquil.

The holotype (plate 3, figure 3a-c) is a tumid, thick-walled test consisting of three whorls, with five chambers surrounding the proloculus in the first whorl, the second whorl composed of four chambers, and the last whorl made up of five chambers. The chambers arc globose and their peripheries are broadly rounded. The test is wholly involute ventrally but is evolute dorsally except for partial involution developed by the last-formed chamber of the last whorl. The walls of the chambers are smooth and wholly perforate, except for a granular, secondarily imperforate area on the ventral side of the test immediately facing the aperture.
Dorsally, the wall is thicker over the earlier whorls, which are also the more coarsely perforate exteriorly; progressively later chambers possess thinner walls which are progressively more finely perforate exteriorly. The pore size and distribution is very similar on both the ventral and dorsal surfaces of each chamber of the last whorl, with the exception of the areas of the earlier chambers adjacent to the aperture. The dorsal spiralsuture and intercameral sutures are but little depressed growth laminae of shell material, but they become increasingly depressed towards the last-formed chamber. The spiral suture, like the periphery of the test, is lobulate. The intercameral sutures, at their inner ends, meet the spiral suture approximately at right angles; but at their outer ends they are smoothly recurved, except between the chambers of the later part of the last whorl, where they become nearly radial concomitantly with the approach of dorsal involution.
Ventrally, the intercameral sutures are depressed and smoothly curved, the chambers completely embracing at their umbilical ends and thus forming a narrow umbilical depression but no true umbilicus. The sutures meet at a point in this umbilical depression (there is no linear suture), and they become sigmoidally curved as they traverse its limits. The aperture is a very low, ventral, interiomarginal arch, extending along the base of the very low apertural face from about the periphery of the first chamber of the last whorl almost to the anterior intercameral suture of the second chamber of the last whorl. The aperture possesses no lip, but the inner margin of the apertural face is convex, thickened, hyaline and rimlike. The narrowness and convexity of the apertural face causes the aperture to be slightly set back as a continuously developed re-entrant, below and posterior to the anterior surface of the apertural face. The maximum diameter of the test is 0.48 mm.; its maximum thickness is 0.40 mm

References:

Banner, F. T. & Blow, W. H. (1967). The origin, evolution and taxonomy of the foraminiferal genus Pulleniatina Cushman, 1927. Micropaleontology. 13(2): 133-162. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Pulleniatina obliquiloculata praecursor Banner & Blow 1967

Pulleniatina obliquiloculata praecursor

References:

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