MEXICAN DOCK WORKERS warn scuba diving tourists about the “enchantment of the depths,” a deadly kind of disorientation induced by the aqua blues, greens, and fluorescent yellows seen beneath the surface of the sea. Some divers are so seduced by the Caribbean’s clarity even at several hundred feet below the surface that they simply forget to come up.If we hadn’t been obliged to bring these photographs back from Isla Mujeres, an eight-kilometer ferry ride from Cancun, we wouldn’t have come back either. We thought about opening a regional magazine office in a thatched hut, where we could work with salty sand in our ears and pull back a few Tres Equis before noon. Lord knows we had enough bathing suits to last a lifetime, or at least until Dallas merchants start selling next year’s luscious lines. We’re saluting the most sophisticated swimwear designers by presenting their best and brightest-the looks that will make you the enchantress of Lake Dallas, Ray Hubbard, or the palm tree-shaded, bleached white beaches along the Mexican coast. (Continued on page 149)If you can’t find a conch shell, you can hoist an old penny loafer to your ear and hear the same ocean reminding you that Cancun and other Mexican cities are still inexpensive places for Texans to visit. Finding a flight that coincides with your vacation plans is getting easier to do, now that Texas International Airlines has become the only U. S. carrier to schedule Pacific coast connecting services from Houston to Manzanillo, Puerto Vallarta, and Ixtapa. Daily direct and connecting flights are also available from Dallas to Monterrey, Mexico City, Guadalajara, Cancun, Cozumel, and Merida. Call Action Tours, 748-2581, for information about Peanuts Fares, special flight times, group rates, and hotels.