ace books mmpb first printing, first p/b edition
half a classic ''ace double'' format mmpb with two front covers, contents tête-beché to each other
cover art by ed emshwiller (signed emsh, uncredited)
cover price 35¢
½ 320pp. (~143pp.) including 2 x titles, indicia etc, advertising pp. in-between the double's halves
doubled with "city under the sea" by kenneth bulmer, q.v.