Calculites tetraplevros
SEM photo of Calculites tetraplevros from Farhan et al. 1994 (Pl. 1, Fig. 12)
Set number: 3008
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10µm
Set number: 2997
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10µm
Calculites tetraplevros Varol, in prep.
From the Greek tetraplevros, meaning “quadrilateral”, referring to the quadrilateral cross-section of the distal process.
Elliptical species of Calculites are constructed of a narrow outer wall and four central crystalline blocks that support a large, hollow distal process, quadrilateral in cross-section and aligned longitudinally. The process is supported by four to five struts arising from the corners and produces large depressions between adjacent struts. The scanning electron microscope image illustrated in Plate 1, Figure 12, of Farhan et al. (1994) provides the best example of this detailed structure.
The diagonal sutures extending from the centre between the crystalline blocks may curve gently towards the periphery.
In plan view under crossed polars, the outer wall and the crystalline blocks display first-order whitish-yellow interference colours, whereas the distal process exhibits yellow interference colours.
Calculites tetraplevros exhibits parallel extinction (extinction angle 0°) and length-slow (+) elongation in its natural position.