Man from Atlantis - Season 1 - Eps 6: Shoot-Out at Land's End
Mark is somehow linked with a man named Billy, existing in a wild west town, who appears to be his twin. Investigating, Mark arrives in the town and discovers that Billy once had the same webbing as Mark, but also that he has had it removed.
About Man from Atlantis

Title: Man from Atlantis
First Air Date: 1977-09-22
Last Air Date: 1978-06-06
Status: Canceled
Rating: 6.4/10 (from 64 votes)
Language: EN
Seasons: 2
Total Episodes: 13
Network: NBC
Genres: Sci-Fi & Fantasy, Drama, Action & Adventure
Production Companies: Solow Production Company
Synopsis
Atlantis survivor Mark Harris breathes underwater, withstands extreme depth pressures and wields superhuman strength.
Cast

Patrick Duffy
Mark Harris

Belinda Montgomery
Dr. Elizabeth Merrill

Alan Fudge
Dr. Crawford

Jean Marie Hon
Jane