Hans-Pény Hirmenech was the author of a 1906 book, in French, in which he reviewed possible connections between the Celts, Basques and Atlantis. He claimed that Atlantis had been situated in the North Sea and that Helgoland was a remnant of it.
Hirmenech expressed the wild idea that the rows of standing stones at Carnac marked the tombs of Atlantean soldiers who fought in the Trojan War!
Hirmenech was a founding member of la Société Préhistorique Française (The Prehistoric Society of France)(a).
[I’m indebted to Stelios Pavlou for some details above.]