From the publishers - The Amphibian Man by Alexander Belyaev

The Amphibian will throw you back to a time when skin and deep-sea diving had not yet made the Silent World begin yielding up its secrets on a really big scale, as aqualung and snorkel are doing today, and present to you Alexander Belyaev’s 1928 prevision of the ocean mastered by mankind.
Sea-devil has appeared in the Rio de la Plata. Weird cries out at sea, slashed fishermen’s nets, glimpses of a most queer creature astride a dolphin leave no room for doubt. The Spaniard Zurita, greed overcoming his superstition, tries to catch Sea-devil and force it to pearl-dive for him but fails.
On a lonely stretch of shore, not far from Buenos Aires, Dr. Salvator lives in seclusion behind a high wall, whose steel-plated gates only open to let in his Indian patients. The Indians revere him as a god but Zurita has a hunch that the god on land and the devil in the sea have something in common. Enlisting the help of two wily Araucanian brothers he sets out to probe the mystery.
As action shifts from the bottom of the sea to the Spaniard’s schooner The Jellyfish and back again, with interludes in sun-drenched Buenos Aires and the countryside, the mystery of Ichthyander the sea-devil is unfolded before the reader in a narrative as gripping as it is informative.
Alexander Belyaev, the first-and very nearly the best-Soviet science-fiction writer, was born in 1884 in Smolensk. When a little boy Alexander was full of ideas. One of them was to fly. And he did fly — from a rooftop — until one day he fractured his spine. This was put right, but at the age of 32 he developed bone tuberculosis and was bed-ridden for nearly six years and later for shorter stretches.
After school he studied law and music. To pay for his tuition he played in an orchestra, designed stage settings and did free lance journalism, which he continued after graduation. In 1925 he gave up law and devoted himself wholly to writing.

His first novel, Professor Dowell’s Head, serialized in a popular magazine in 1926, was an immediate success. Since then A. Belyaev wrote fifty-odd novels — many of them as topical as if written today — reaching the one-million copy mark by January 1942 when he died near Leningrad (now St. Petersburg). His best known books are The Amphibian, A Jump into Nothingness and The Island of Dead Ships.