American Authors and Critics
Barnes & Noble had a hand in this series for its duration, initially publishing it 1961-1964 from AC 1 to AC 10 (excepting AC 9, which was evidently never released) but later only distributing it after Holt, Rinehart and Winston took over publication from 1967-1970. Holt evidently republished some of the earlier volumes, hence the varying styles in cover design. The AC- prefix was dropped when Holt picked up the series.
Barnes & Noble Paperbacks in American Literature, PW, Dec. 28, 1959, at 49 (announcing the American Authors and Critics Series, to be launched in the fall of 1960, although they actually didn't publish until the following fall).
Ad, PW, Oct. 3, 1960, at 19-22 (showcasing the launch of both the American Authors and Critics Series and the University Paperbacks).