Cingulum is a term that refers to all of the collective elements of the diatom girdle. The cingulum is made up of delicate silica bands (= girdle bands, copulae) that join the two valves of a frustule. Most diatoms possess a cingulum, although some may not. The silica structures of the cingulum may be secreted after vegetative cell division that produces the diatom valve; that is, while the deposition of the silica valves are tied to cell division, the deposition of the cingulum may not be tied to division.
All of the girdle bands make up the cingulum.
All of the copulae make up the cingulum. The first copula (the one positioned next to the valve) is termed the valvocopula.
Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.