Calculites ovalis

Tetralithus ovalis Stradner, 1963

Elliptical species of Calculites are constructed of a narrow outer wall and four central crystalline blocks that support a very narrow, solid distal process. The sutures between the crystalline blocks meet at the centre, forming a cross that is rotated slightly relative to the long axis of the ellipse.

In this holococcolith, in plan view under crossed polars, the outer wall and the crystalline blocks display first-order brownish-yellow interference colours.

Calculites ovalis exhibits parallel extinction (extinction angle 0°) and length-slow (+) elongation in its natural position.

Sissingh, W. 1977. Biostratigraphy of Cretaceous calcareous nannoplankton. Geologie en Mijnbouw. 65(1): 37-65.

Stradner, H. 1963. New contributions to Mesozoic stratigraphy by means of nannofossils. Proceedings of the Sixth World Petroleum Congress. Section 1 Paper 4: 167-183.