  By the construction of suitable non-metabelian Schur sigma-groups S of type
(9,3) with log order lo(S) = 21 and nilpotency class cl(S) = 9, evidence is
provided of a new class of imaginary quadratic fields K with 3-class group
Cl(3,K) ~ C(9) * C(3) and punctured principalization type kappa ~ (1,4,4;4)
whose 3-class field tower consists of precisely three stages. In contrast,
previous examples of three-stage towers were associated with kappa in {
(1,1,2;2), (1,1,2;3), (1,1,4;2), (1,2,3;1) }, lo(S) = 9 and cl(S) = 5.
