ABSTRACTSeveral papers regard the anatomy of the peripheral olfactory organ, the olfactory rosette, in the class of Chondrichtyes. The complex shape of this organ and the differences among species give clues to functional, evolutionary, and ecological observations; data on a larger number of species are needed in order to have a more complete insight. The rosette is made up of a central support and of numerous lamellae, which are lined by the sensory epithelium. The size, shape and number of these lamellae, which are highly variable among species, are noteworthy because they affect the sensory surface area, the water dynamic within the olfactory chamber, and the organization of the olfactory bulb. In the literature about Chondrichthyes, the definition of olfactory lamella is confused, because authors use the same words for different structures. The average number of lamellae is distinctive for each species, and the meaning of this difference is not completely understood and, in this frame, a not unambiguous definition of lamella leads to difficulties in comparing data from different publications and analyzing them together. We aim to give here an unambiguous definition of olfactory lamella, that should be each single fold of tissue extending from the raphe, and of lamellar number of a given species, that should be the average number of lamellae in one olfactory organ. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:2039–2045, 2017. © 2017 Wiley Periodicals, Inc.