Under a dirty, sagging tarp, in a back yard on Belmont, 30 some old men have gathered to look at half-naked ladies.

They are vintage paperback collectors and the ladies are bikini-clad Amazons and sultry-looking nymphos on the covers. Vintage paperbacks are the small, pocket-sized books published between 1938 and 1968. The steamier ones have titles like Negligee: An Uncontrolled Torrent of Seething Passion, and Tortured Love: Her Flesh Longed for a Man to Tame Her. Raw, mid-century, pop culture. The good old days.

The old men have come from up and down the coast for Lance-Con, a trade show put on by Lance Casebeer, known to many as the godfather of paperbacks. His is the only complete collection of vintage paperbacks in existence. Lance-Con is in its 24th year now. Some of the collectors have made it to 20.

The vintage paperback era started with Pearl Buck's The Good Earth in 1938 and lasted until the late 1960's, publishers started using computer numbers instead of serial numbers. But even by the late 1950's, women began to overtake men as paperback readers, and publishers started putting the women on the covers in more clothes.

It was the beginning of the end. Half-naked ladies aren't the only reason these men have gathered here, but they are a big part. Because at Lance-Con, you can judge a book by its cover. "Right now, sleaze is the big thing," says Gyenis. "No one reads these books. It has more to do with the cover and the title. The more outrageous the title, the better."

One of Lance-Con's attendants is writing a book on the famous cover artist Robert McGinnis, who did over 1,100 paperbacks covers and is still alive. Every year he comes to the New York Paperback Show to sign his books.

There are also collectors interested in the literature. Gyenis first got into collecting while looking for a copy of Canary In A Cat House, by Kurt Vonnegut. The book was reprinted as Welcome to the Monkey House, but one story was left out. Atilla wanted that story. He has five copies now, and is considering buying a sixth. He can't help himself. "We're nuts," he says. "It's all compulsion. That's what it's all about."

Compulsion, nostalgia, and women in underwear. This year, despite the jokes and laughing and trading under the blue tarp, there is an undercurrent of melancholy. Price guides have driven up prices. The completists who collect entire publisher runs, like Casebeer, Lesser, and Green, are getting out or dying off. And Lance-Con, which once took up three back yards, is down to 10 tables. The state of collecting is in decline.

"For me personally," says Gyenis, "I'm on my way out. You can't find the stuff. You can't replenish stock. You don't have the completists you did 10 years ago." There are few younger collectors. (Casebeer says his son has never read a book, and is proud of it.) And the days when good, cheap finds were hidden in every bookstore are gone.

It's too expensive to get into the trade now. The decline, however, will be gradual and won't be complete for some time yet. Lance-Con will come around at least one more time, at next year's 25th anniversary. Casebeer expects it to be the biggest paperback conference ever. People from around the world are already booked.

If he's right, it may be the last time Lance-Con fills three backyards with old men laughing and joking, buying and selling, and remembering the days when men were men, women were half-dressed, and a good book never cost more than a quarter.