Ellipsagelosphaeraceae
Ellipsagelosphaera Noël, 1965
Watznaueriaceae Rood et al., 1971
Circular to elliptical placoliths have single-tiered distal and proximal shields and a double tube cycle. The central area may or may not be occupied by structures. Differentiation of the tube cycles can be challenging under a light microscope; however, identification is facilitated under phase-contrast or bright-field illumination, particularly where the outer tube cycle differs slightly in height from the inner tube cycle and the distal shield.
In plan view under cross-polarised light, all components display inclined extinction lines and length-fast (–) elongation. Variations in the orientation of extinction lines aid in distinguishing the outer and inner tube cycles, as they commonly exhibit different extinction angles.
Noël, D. 1965. Sur les Coccolithes du Jurassique Européen et d'Afrique du Nord. Essai de classification des coccolithes fossiles. Éditions du Centre National de la Recherche Scientifique, Paris. 1-129.
Rood, A. P., Hay, W. W. & Barnard, T. 1971. Electron Microscope Studies of Oxford Clay Coccoliths. Eclogae Geologicae Helvetiae. 64: 245-272.
