First US edition of The Twilight of Briareus, published in 1974 with a jacket design by Mike Stromberg. All text is set in the bold weight of Leo Castriota’s Flat Top. The interior (not shown here) is set in Times New Roman.

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First-edition jacket for The Twilight of Briareus, featuring Gary Gillot’s Embrionic Triline for the title. John Middleton Murry Jr. (1926-2002) wrote the science-fiction novel under his pseudonym Richard Cowper. From Wikipedia:

According to Cowper, he wrote the book almost immediately after his novel Kuldesak was published successfully in 1970, and Twilight was “a more substantial work in every way”. His publishers rejected it, and despite his discouragement he started the novel Clone with the idea of satirising science-fiction people who did not like Twilight. His publishers accepted it and it sold well, after which they accepted Twilight, which sold even better.

[More info on ISFDB]