Article: Shell structure of the billingsellacean brachiopods

Sections of Cambrian articulate brachiopods from the U.S.S.R. show that the calcareous shell of the billingsellacean Nisusiidae probably consisted of normally developed primary and secondary layers with orthodoxly stacked fibres. Disposition of the recrystallized fibres further suggests that whereas Nisusia was impunctate, the related Kotujella was permeated by simple canals which must have been indistinguishable from the caeca accommodated within endopunctae of younger, unrelated articulate brachiopods.