Thanaroa is, I suspect, the original form of the name of Tangaroa, the greatest god of the Polynesians.

There's a secret cult to him in the islands.
Marakinoff may belong to it--he knows it anyway.

Lugur recognized the signal and despite his surprise answered it." "So he gave him the high sign, eh ?" mused Larry.

"How could they both know it ?" "The cult is a very ancient one.

Undoubtedly it had its origin in the dim beginnings before these people migrated here," I replied.