  The Fuss-Catalan numbers are a generalization of the Catalan numbers. They
enumerate a large class of objects and in particular m-Dyck paths and m+1-ary
trees. Recently, F. Bergeron defined an analogue for generic m of the Tamari
order on classical Dyck words. The author and J.-Y. Thibon showed that the
combinatorial Hopf algebras related to these m-Tamari orders are defined thanks
to the same monoid, the sylvester monoid, as in the m=1 case and that all
related Hopf algebras also have m analogues.
  We present here the m-generalization of another construction on Catalan sets:
the dendriform algebras. These algebras are presented in two different ways:
first by relations between the m+1 operations, relations that are very similar
to the classical relations; and then by explicit operations splitting the
classical dendriform operations defined on words into new operations. We then
investigate their dual and show they are Koszul.
