  We describe a set $\mathcal{R}^{\infty}$ consisting of tuples of integer
sequences and provide certain explicit maps on it. We show that this defines a
semiregular crystal for $\mathfrak{sl}_{n+1}$ and $\mathfrak{sp}_{2n}$
respectively. Furthermore we define for any dominant integral weight $\lambda$
a connected subcrystal $\mathcal{R}(\lambda)$ in $\mathcal{R}^{\infty}$, such
that this crystal is isomorphic to the crystal graph $B(\lambda)$. Finally we
provide an explicit description of these connected crystals
$\mathcal{R}(\lambda)$.
