In both cases, the R structure is indicated as a direct product of one covariance matrix and one correlations matrix, using a period to separate the two components. Recall that we want the R structure to have variances on the diagonal and this is produced from a direct product between a covariance matrix (which has variances on the diagonal) and a correlation matrix (which usually has ones on the diagonal). A direct product between two correlation matrices would not work because it would be scaled to ones on the diagonal instead of the residual variance.