Bay_City_Rollers

Alan Longmuir, a founding member of the Scottish pop group the Bay City Rollers, which enjoyed huge commercial success in the 1970s, died on Monday in Scotland. He was 70.

His family announced his death but did not specify where he died or give a cause. He had been receiving medical treatment in Edinburgh after being flown home from Mexico, where he fell ill while on vacation.

The Bay City Rollers, known for their tartan outfits and their upbeat, catchy tunes like “You Made Me Believe in Magic” and “I Only Want to be with You,” had a fanatical teenage following and sold more than 100 million records worldwide. Although they were always bigger in Britain, they also had seven Top 40 singles in the United States, including “Saturday Night,” which reached No. 1 in 1976. The group is a staple on "The Lost 45s" show and made an appearance in concert in Boston for the program.

Mr. Longmuir, who played bass and occasionally keyboards, formed a band called the Saxons in 1966 with his brother Derek, a drummer, and others. The band underwent numerous personnel changes before settling on its best-known lineup in 1974, with the Longmuir brothers joined by Les McKeown as lead singer and Eric Faulkner and Stuart Wood on guitars. They were said to have chosen the name Bay City Rollers by throwing a dart at a map, which landed on Bay City, Mich.

Mr. Longmuir left the group in 1976, citing stress. (“I was getting depressed,” he told the BBC in 2015. “I couldn’t take it anymore.”) He walked away from the music business entirely, working as a plumber and a water pipe inspector.

After more personnel changes, the band shortened its name to the Rollers in 1978 and continued for a few years before disbanding. Various combinations of former members toured as the Bay City Rollers over the years, and Mr. Longmuir, Mr. McKeown and Mr. Wood reunited in 2015 for a string of sold-out performances.

Alan Longmuir was born on June 20, 1948, in Edinburgh. Survivors include his wife, Eileen, and his brother.