  If $N=2^k > 8$ then there exist exactly $[(k-1)/2]$ pairwise nonequivalent
$Z_4$-linear Hadamard $(N,2N,N/2)$-codes and $[(k+1)/2]$ pairwise nonequivalent
$Z_4$-linear extended perfect $(N,2^N/2N,4)$-codes. A recurrent construction of
$Z_4$-linear Hadamard codes is given.
