Graphs, showing the relation of the primary chambers to the number of their secondary chamberlets, demonstrate that Tan's nepionic mutants are variable, even in the course of a short period. The evolutionary change of the nepionic mutants is consistent with the evolutionary change of Cycloclypeus as a whole. The number of secondary chamberlets of the first neanic chamber is considered a valuable characteristic for the identification of species. Reduction of the number of nepionic chambers in the course of time is thought to result from the occurrence of 'transitional nepionic variants'.