American Heritage Series
According to PTLA, AHS 1 was published in 1954 by the Liberal Arts Press, although PTLA also says AHS 5 was published in 1953. Maybe the titles were published out of order?
It appears that Bobbs-Merrill-published titles probably started with AHS 24, although it appears that subsequent titles were published out of order as well (e.g., AHS 31 came out in 1973 but AHS 32 in 1966).
Liberal Arts Press Merges with Bobbs-Merrill, Publishers Weekly, Jan. 16, 1961, at 97:
Ad in 1974 Program of the Annual Meeting of the American Historical Association: