Which book is this?
I think even Pope Pius XII banned this in the very early 1950's. I don't think this style has been worn by anyone (priests, bishops, Cardinals or even the Pope), since the late 1940's or very early 1950's.I know that Pius XII banned Cardinal's cappa magna trains longer than 9 feet in 1954, but John XXIII allowed trains as long as 12 ft. back again as soon as he took over.
I myself saw it worn in Italy by a prelate in 2008.
"worn by anyone ...1940's or very early 1950's."It was nice usance until the late sixties.
Bishop Slattery's cappa at the TLM in Washington DC had to be at least twenty feet long.
I think it is from John Nainfa pss "Costume of Prelates of the Catholic Church". This book, published in 1926, is available on line (free of charge), around 350 pages with many pictures).
Train on the choir cassock was abolished in 1953. See here.