CATALOG OF ORIGINAL DESCRIPTIONS: Globotruncana stephensoni Pessagno 1967
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Citation: Globotruncana stephensoni Pessagno 1967Taxonomic rank: speciesType specimens: Plate 69, figures 1-7; Plate 96, figures 5, 6; 689269Type sample (& lithostrat): Upper Taylor MarlType locality: From sample TX 291-B, collected from a ditch crossing Sate Route 73, 2.4 miles east of the intersection of Route 73 with Farm Road 737, Prairie Hill, Limestone County, TXType repository: Washington; USNM
Original Description Trochospiral, spiroconvex; periphery sharply angled with narrow double keel merging to form a single keel in the last whorl; rare specimens single-keeled entirely in final whorl, but when sectioned showing double keel in preceding whorl; double keel when present, strongly reflected umbilically. Test having about three whorls of chambers which slowly expand in size; 6-7 chambers in the last whorl. Chambers spirally, typically trapezoidal to subtrapezoidal, but often petaloid, cresent-shaped, or subtriangular, separated by straight to slightly curved, raised, often beaded sutures. Chambers individually smoothed surfaced, containing few if any rugosities. Umbilicus deep and wide; surrounded by umbilical shoulder which may or may not be beaded; umbilicus covered by spiral system of tegilla having intralaminal and infralaminal accessory apertures. Primary aperture interiomarginal, umbilical in position. Outer wall radial hyaline, perforate except for keels. Keels when single predominantly radial hyaline, imperforate; when double in part radial hyaline, imperforate, and ultragranular hyaline, imperforate; umbilical rim of double keel weak, entirely ultragranular hyaline, imperforate; spiral rim with radial hyaline, imperforate base which is strengthened by accretion of ultragranular hyaline outer portion. Septal walls and tegilla microgranular hyaline, finely perforate. Etymology: named in honor of the late L. W. Stephenson in recognition of his great contributions to the study of the Cretaceous stratigraphy
of the Atlantic and Gulf Coastal Plains Extra details from original publication
1931. Globotruncana arca (Cushman),Plummer (part). Univ. Texas Bull. 3101. pp. 195-198. pl. 13. figs. 7a-c: not figs. 8. 9, 11.
1957. Globotruncana (Globotruncana) arca (Cushman). Edgell (part). Micropaleont. vol. 3. No.2, pp. 110-111: pl. 1, figs. 10-12: not pl. 3. figs. 1-3. 13-15.
1962. Globotruncana conica White, Pessagno. Micropaleontol, vol. 8. No. 3. p. 302, text-fig. 4. pl. 4. figs. 13. 14.
1963. Globotruncana (Globotruncana) rosetta rosetta (Carsey), Van Hinte (part), Jahrb. Geol. Bund.. Sond. 8. pp. 89-91, pl. 9. figs. 1-2: not pl. 9, figs. 3: pl. 10 fig.1
Remarks: G. stephnsoni Pessagno, n. sp. is closely related phylogenetically to G. arca (Cushman). Ephehic individuals of G. stephensoni n. sp. differ from those of G. arca having approximately the same diameter by (1) possessing angled peripheries; (2) narrow double keels which merge to form a single keel in the last whorl; and (3) by usually having more trapezoidally shaped chambers. Both species possess double keels which are strongly reflected umbilically and have similar structure (TYPE 1; Text-figure 40). G. stephensoni, n. sp. may be perfectly homeomorphic externally for either high-spired forms of G. stuarti (de Lapparent) s.s. or for G. conica White and can only be separated in thin-section from these latter species. Most Campanian and Early Maestrichtian occurrences of G. conica and G. stuarti (de Lapparent) s.s. most likely represent occurrences of G. stephensoni, n. sp. For example, Pessagno (1960, p. 91, chart 2: 1962. p. 355. chart 1) noted G. conica in Puerto Rican strata of Late Campanian and Early Maestrichtian age. The sectioned specimen figured as G. conica White by Pessagno (1962, text-figure 1, p. 362) resembled G. conica externally. It posessed subtrapezoidal chambers spirally and showed a spiroconvex test. However, it also showed a narrow double keel in the posterior portion of the last whorl and in the preceding whorl.
References:
Pessagno, E. A. (1967). Upper Cretaceous planktonic foraminifera from the western Gulf Coastal Plain. Palaeontographica Americana. 5: 245-445. gsO
Globotruncana stephensoni compiled by the pforams@mikrotax project teamviewed: 11-2-2025
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