Herb, R. (1978). Some species of Operculina and Heterostegina from the Eocene of the Helvetic nappes of Switzerland and from Northern Italy. Eclogae Geologicae Helvetiae. 71: 745–767.
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Herb, R.
1978
Some species of Operculina and Heterostegina from the Eocene of the Helvetic nappes of Switzerland and from Northern Italy