  The charge ordering in the bilayer manganite system
La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ with $0.30 \le x \le 0.50$ has been
studied by neutron diffraction. The charge order is characterized by the
propagation vector parallel to the [1 0 0] direction (MnO$_2$ direction), but
the correlation length is short-ranged and extremely anisotropic, being $\sim
0.02a^{*}$ and $\sim 0.2a^{*}$ parallel and perpendicular to the modulation
direction, respectively. The observed charge order can be viewed as a
quasi-bi-stripe order, and accounts well for the $x$ dependence of the
resistivity. The quasi-bistripe order is stable within the ferromagnetic (FM)
MnO$_2$ layers in the A-type antiferromagnetic order, but is instabilized by
the 3 dimensional FM order.
