An error has been noted within Fig. 1 of the paper by Howard & Stokes (1998) . There is a group-subgroup relationship between I4/mcm (a⁰a⁰c^-) and C2/c (a^-b^-b^-), and this should be indicated on the figure by a continuous line joining the corresponding boxes. The corrected version of the figure is shown here.

Figure 1 A schematic diagram indicating the group-subgroup relationships among the 15 space groups tabulated by Howard & Stokes (1998). A dashed line joining a group with its subgroup indicates that the corresponding phase transition is required by Landau theory to be first order.