Amended diagnosis of Colveraia variabilis Klinghardt, 1921 (Bivalvia) from Friuli (NE Italy) and redescription of Colveraia darendeensis Karacabey, 1974 from Turkey: Taxonomy, comparisons and biogeography

An examination of the historical material of Colveraia variabilis Klinghardt, 1921 housed in the collections of the Steinmann Institute of Palaeontology (Bonn, Germany) and of some newly collected specimens from the type area of Mt. Jouf (Friuli, NE Italy) has revealed many previously unknown characters of this radiolitid. Klinghardt had only large fragments of Colveraia variabilis at his disposal and he erred in some respects, mainly by mistaking the upper valve for the lower one. Representatives of the genus Colveraia have been collected at different localities of the Central-Eastern Mediterranean Tethys and the Arabian Plate, but the majority of these have never been described in detail or have been identified solely on the basis of transverse sections, except in Turkey, where many well-preserved specimens have been recovered. Historical and new examples of Colveraia variabilis from Mt. Jouf and the material recovered from Turkish localities show different external characters as far as radial zone, general shell shape and ornamentation are concerned. These lead us to assign all Turkish specimens to Colveraia darendeensis Karacabey, 1974, which is here described in detail. Comparisons with congeneric forms from the Central-Eastern Mediterranean Tethys and the Arabian Plate are also made.