Line of sight velocity dispersion in 574 clusters and rich groups of galaxies as a function of the apparent elongation q_2D. The blue error bars show the mean 68 per cent uncertainties of the measurements. The black points show the mean and the 68 per cent scatter of the dispersions in 5 bins of the elongation. The velocity dispersions are scaled by the characteristic velocity V_c which is a measure of the gravitational potential depth of the host dark matter haloes. The figure shows that circular clusters exhibit higher normalised line of sight velocity dispersions than elongated ones.