On a routine expedition high in the rapids, the Butler family passes through a whirlpool and emerges in a mysterious lost world where prehistoric animals dwell. Befriended by a caveman clan, the Butlers learn to cope with life in the adventure-filled valley as they try to find the way back home, in this 1974-75 Hanna-Barbera animated series. 16 episodes on 2 discs. 5 3/4 hrs. Standard; Soundtrack: English Dolby Digital mono.