Local limit theorem for triangular array of random variables

For a triangular array of random variables $\{X_{k,n}, k=1, \ldots, c_n; n\in{\mathbb N}\}$ such that, for every $n,$ the variables $X_{1,n},\ldots,X_{c_n,n}$ are independent and identically distributed, the local limit theorem for the variables $S_n = X_{1,n} + \ldots + X_{c_n,n}$ is established.