ACTION COMICS 244 came out a day after I was born. This one featured "The Super-Merman of the Sea" written by Otto Binder, with art by Curt Swan and Stan Kaye, who also did the cover. It's interesting to compare Swan's art on this story with the work he did on the AQUAMAN mini-series in the '80s.
Only two weeks before ACTION 244, BATMAN 118 came out, cover featuring "The Merman Batman" with the cover by Swan and Kaye, as well. The actual inside story was by Finger, Moldoff and Paris.