ABSTRACT
Comparison of thecal plating of Rhipidocystis and Cryptocrinites shows that these genera have been closely related. Some differences in the plating were caused by the process of theca flattening in Rhipidocystis. The bend of the theca in both genera in the same plane of symmetry but in opposite directions as well as the different position of anus resulted from the process of heterochrony.
