- according to Hottinger (2006):
SEPTULUM - (French: cloisonette); endoskeletal, wall-like partition extending from the lateral wall into the chamber lumen, dividing it into compartments (chamberlets). In imperforate forms, these partitions are produced by local thickening of the inner part of the shell wall. Their disposition has a close relation to the arrangement of the foramenal axes. In lamellar-perforate species, the septula are produced by folded inner lamellas.
Remarks: In describing alveolinid structures, there has never been any difficulty in distinguishing between a septum (closing off a chamber) and a septulum (partitioning the chamber into chamberlets) ever since Carpenter (1862), Douvillé (1906) and Reichel (1936-1937). In orbitolinids however, there is considerable confusion. Carpenter (1862) described "Patellina" (= Orbitolina) lenticularis with a "large chamber layer". This term corresponds in modern terminology to a single, discoidal (or annular) chamber separated from the next "layer" by a septum. R. Schroeder kept up the idea of the chamber layer to at least 1973 but abandoned it in his 1975 paper. The concept of a chamber layer in orbitolinids leads to the interpretation of the orbitolinid radial partition as "septum" and of secondary, exoskeletal partitions as a "septulum" which is inconsistent with the structural interpretation of all other imperforate foraminifera. In French papers, where the orbitolinid mode of growth was correctly recognized as a uniserial stack of chambers, we find the simultaneous use of septum (for the true septum), cloison for endoskeletal radial main partitions and cloisonette (for beams in the exoskeleton).
Carpenter, Parker & Jones (1862), Introduction to the study of Foraminifera, Ray Society, London, 319 p. + 22 pls.
Douvillé (1906), Évolution et enchaînement des Foraminifères, Bulletin de la Société géologique de France, Paris, (4ème série), tome 6ème, p. 588-602 + pl. XVIII.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744 Reichel (1936-1937), Étude sur les Alvéolines, Mémoires de la Société paléontologique Suisse, Bâle, vols. LVII & LIX, 147 p. + 11 pls.
Schroeder (1973), El corte de Aulet (Prov. de Huesca) Evolucion de las Orbitolinas en el limite del Cretaceo inferior superior. In: XIII Coloquio Europeo de Micropaleontologia España 1973, Enadimsa, Madrid, p. 141-149.
Schroeder (1975), General evolutionary trends in Orbitolinas, Revista Española de Micropaleontologia, Madrid, Numero Especial (1975), p. 117-128.