The second species is known locally under the name _concha nacar_, and has been named _Margaritifera_ (_Avicula_) _vinesi_ (Rochebonne).[298] It occurs only in the northern part of the gulf near the mouth of the Colorado River. Formerly it was abundant in that region, occurring in large areas, but it has become much reduced and is now little sought after. It is claimed that this species is far more productive of pearls than the _M. margaritifera_, and that it yielded the large quantities obtained by Osio in the eighteenth century. Although iridescent, the shell is so thin and convex that it is without commercial value. [Illustration: THE ADAMS GOLD VASE Ornamented with American gems and fresh-water pearls, rock crystal, gold quartz and agatized wood Top of vase and side view Now in the Metropolitan Museum of Art ] The headquarters of the Mexican pearl fishery are at La Paz, the capital of Lower California, 240 miles northwest of Mazatlan and 150 miles north of Cape San Lucas. This “Mantle of Peace”—the literal translation of La Paz—contains about 5000 inhabitants, nearly all of whom are more or less dependent on the pearl fishery. It presents an attractive picture, with the cocoanut-palms extending down almost to the water’s edge, and the high mountains forming a background. The low, stone houses, the tile roofs, the plaza with tropical trees, and the beautiful flower beds under perennial sunny skies, give it a quaint appearance. The most conspicuous objects from the harbor are the large old warehouses, with thick walls and iron-barred windows, for the storage of the pearls and the shells. During the season, from April to November, the arrival and departure of the pearling vessels presents a scene of great animation. The present methods of the fishery on the Mexican coast are quite different from those of thirty years ago when nude diving was the only method in vogue. Instead of the haphazard work, largely in shallow water, the industry is conducted systematically, and the limit of depth is increased, much of the diving being in depths of ten to fifteen fathoms. The fishermen operate either from a large vessel making a cruise two or three months in length, or from a camp on the shore near the reefs. A vessel visits them frequently to furnish supplies and to transport the catch to La Paz. The fishing boats are undecked craft, each equipped with an air-pump and a crew of six men: a diver, a _cabo de vida_ or life-line man, who is usually the captain, two _bomberos_ at the air-pump, and two rowers.