  We discuss an extension of the super-Poincar\'e algebra in $D=11$ which
includes an extra fermionic charge and super two-form charges. We give a
geometrical reformulation of the $D=11$ supermembrane action which is
manifestly invariant under the extended super-Poincar\'e transformations. Using
the same set of transformations, we also reformulate a superstring action in
$D=11$, considered sometime ago by Curtright. While this paper is primarily a
review of a recent work by Bergshoeff and the author, it does contain some new
results.
