The skeletal architecture of conodonts of the order Prioniodinida Sweet, 1988, is poorly understood. Undisturbed or slightly disturbed natural assemblages are rare. A three-dimensional apparatus plan has been constructed using scale models of the elements of Idioprioniodus, based on late Mississippian and late Pennsylvanian (Carboniferous) assemblages from Montana and Illinois, USA. The interpretation of the architecture is based on symmetry relationships between the various elements. A revised element notation scheme is proposed for the apparatus. □Conodonts, apparatus, palaeobiology, Prioniodinida, Idioprioniodus.