Originally intended to be a trilogy, the third installment was never written. Publications can be confusing as both the first and second installment have been published as ''The World Below''. They are typically paired as ''The Amphibians'' (part 1) and ''The World Below'' (part 2), or as ''The World Below''(part 1) and ''The Dwellers'' (part 2).
Galaxy SF novel #5.
Cover has no attribution, but signed by artist (no signature found (WH), barely visible at the bottom on PV2's copy). Cover artist first name on this book from The Whole Science Fiction Data Base No.2.
