Abstract

"Globigerina cretacea d'Orbigny, described by d'Orbigny in 1840 as the only trochoid Globigerina from the Craie blanche of the Paris basin, began its development in the Aptian-Albian with the form Praeglobotruncana infracretacea (Glaessner); it gradually changed (by enlargement and by change in apertural conditions) into Praeglobotruncana sp. cf. P. gautierensis (Bronnimann) of Bolli, and occurs in the Cenomanian as P. crassa Bolli. Due to the enlargement of the later chambers, the apertural conditions changed gradually, and the developmental stage of typical Globigerina cretacea d'Orbigny was reached, beginning in the Turonian. At the end of the Maestrichtian, aberrant forms appeared, of which Rugoglobigerina rugosa (Plummer) is the most common. Since a single biological unit ('gens') passes through three different 'genera,' at least two of them (Praeglobotruncana and Rugoglobigerina) must be regarded as artificial. This can also be said of the different 'species.' The gradual cha

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