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Fromea xantha
Plate 2, figures 1–6
Derivation of name
After the characteristic clear yellow wall color (Gr. xantha = yellow).
Holotype: Plate 2, figure 1. ARCO Kalubik No. 3 well, 6750-6780 ft., slide 1, EF U37/1, 141.7 µm apex–antapex.
Description
Large cyst, elongated, single-layered, wall smooth, uniformly thin (∼1 µm), commonly nearly transparent and of a vitreous yellow color, widest at mid-point; pylome in apical position, exact configuration uncertain, but wide and lacking marginal rim or thickening; commonly appearing to form a semi-triangular opening; operculum not observed. Antapex generally sharply rounded. A conspicuous longitudinal fold is usually evident, extending from pylome to antapex. A less prominent medial transverse fold is also commonly evident.
Dimensions
85.0–145.0 (120.5 average) µm apex–antapex; 48.4–70.1 (56.2 average) µm pylome width; 75.2–100.2 (85.7 average) µm medial width (20 specimens measured).
Comments
Fromea xantha differs from F. grandis in normally displaying longitudinal and transverse folds, in having a less diaphanous wall and in being much less narrowed at the apex. Fromea xantha differs from F. nicosia in not having a constricted apical pylome, in not showing medial constriction and in being generally larger.
Occurrence
Rare to frequent, Barremian, Kalubik Formation, North Alaska.
Derivation of name
After the characteristic clear yellow wall color (Gr. xantha = yellow).
Holotype: Plate 2, figure 1. ARCO Kalubik No. 3 well, 6750-6780 ft., slide 1, EF U37/1, 141.7 µm apex–antapex.
Description
Large cyst, elongated, single-layered, wall smooth, uniformly thin (∼1 µm), commonly nearly transparent and of a vitreous yellow color, widest at mid-point; pylome in apical position, exact configuration uncertain, but wide and lacking marginal rim or thickening; commonly appearing to form a semi-triangular opening; operculum not observed. Antapex generally sharply rounded. A conspicuous longitudinal fold is usually evident, extending from pylome to antapex. A less prominent medial transverse fold is also commonly evident.
Dimensions
85.0–145.0 (120.5 average) µm apex–antapex; 48.4–70.1 (56.2 average) µm pylome width; 75.2–100.2 (85.7 average) µm medial width (20 specimens measured).
Comments
Fromea xantha differs from F. grandis in normally displaying longitudinal and transverse folds, in having a less diaphanous wall and in being much less narrowed at the apex. Fromea xantha differs from F. nicosia in not having a constricted apical pylome, in not showing medial constriction and in being generally larger.
Occurrence
Rare to frequent, Barremian, Kalubik Formation, North Alaska.