Story across 23 pages, but page 7 is a 2/3-page and pages 14 and 23 are 1/2-pages.
Teaser ad for Showcase (DC, 1956 series) #79, with Dolphin shown in silhouette (by Gil Kane?)
Letters from Allen D. Murdock, Tad Deeley, Harvey Sobel, John "G.L." Potter, and Mike Bissonnette.