Baxter Algebras and Umbral Calculus
  We apply recent constructions of free Baxter algebras to the study of the umbral calculus. We give a characterization of the umbral calculus in terms of Baxter algebra. This characterization leads to a natural generalization of the umbral calculus that include the classical umbral calculus in a family of $\lambda$-umbral calculi parameterized by $\lambda$ in the base ring. 
Li Guo