Discolithus crassus Deflandre in Deflandre & Fert, 1954
Millbrookia Medd, 1979
Timorhabdus Kristan-Tollmann, 1988
Loxoliths characterised by a robust, often broad, single and high zeugoid wall, and a central area exhibiting a range of structures: a narrow opening, as in Crepidolithus crassus and Crepidolithus parvulus (the latter bearing a proximal plate); a wide opening with a non-permanent proximal grill, as in Crepidolithus perforatus; a granulated central area, as in Crepidolithus granulatus; an axial cross, as in Crepidolithus cruciatus; or a distal process, as in Crepidolithus pliensbachensis and Crepidolithus timorensis.
This loxolith group also includes forms with a double-cycle wall and a wide, open central area, as in Crepidolithus cantabriensis, and those bearing a transverse bar, as in Crepidolithus impontus. These double-walled species should be transferred to a new genus.
In plan view under crossed polars, single-walled Crepidolithus exhibits weak birefringence, showing greyish-white interference colours and length-slow (+) elongation when a gypsum plate is inserted into the light path.
In contrast, under crossed polars in plan view, double-walled Crepidolithus exhibits constant extinction in the outer wall, whereas the inner wall displays white interference colours.
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