A monadic algebraA has finite degreen ifA/M has at most 2n elements for every maximal idealM ofA and this bound is obtained for someM. Every countable monadic algebra with a finite degree is isomorphic to an algebra Γ(X, S) whereX is a Boolean space andS is a subsheaf of a constant sheaf with a finite simple stalk. This representation is used to prove that every proper equational class of monadic algebras has a decidable first-order theory.