External plates: Plate covering incompletely one or several perforations of a wall.
Carcass: Part of wall on intervallum side.
Inner wall: Internal part of the skeleton, separating central cavity and skeletal structures, composed by a porous carcass, simple or coated by an additional sheath.
Presence of carcass external plates: inner carcass wall (IW) | |_ Type of carcass external plates (IW) {None (external plates and/or inner wall)} | |_ Shape of carcass external plates (IW) {None (external plates and/or inner wall)} | |_ Rims of carcass external plates (IW) {None (external plates and/or inner wall)} | |_ Direction of carcass external plates (IW) {None (external plates and/or inner wall)}