ABSTRACT: The details of the shell wall ultrastructure of Strictocostella matanzana (Palmer and Bermudez) 1936 and Strictocostella matanzana (Palmer and Bermudez) 1936 perytae subsp. nov. are investigated for the first time. This study shows that the calcareous shell wall of these two subspecies is monolamellar, consisting of one layer of crystals aligned in a radial direction. This fact necessitates changing the taxonomic position of the genus from the class Rotaliata which is characterized by a bilamellar shell wall to the class Nodosariata whose representatives have a monolamellar shell wall. Some other unique details of the shell and wall structure of the two subspecies studied are also described. The suborder Stilostomellina Saidova 1981 is reinstated and its rank is elevated to that of order.