PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES FOURTH SERIES Vol. XXX, No. 16, pp. 309-355, figs. 1-23. December 30, 1966. THE GULF ISLANDS EXPEDITION OF 1966 By George E. Lindsay Director California Academy of Sciences The Gulf Islands Expedition of 1966 was a joint venture by the Cali-fornia Academy of Sciences, and San Diego Natural History Museum, and the Instituto de Biologia of Mexico. Thirteen scientists from those institu-tions participated in the 10-day cruise, 19-29 April, to 13 islands in central Gulf of California. The expedition was financed partly by a grant from the Belvedere Scientific Fund of San Francisco and partly from a National Sci-ence Foundation grant to the San Diego Natural History Museum. The biogeography of the islands of the Gulf of California, and the systematic classification of the organisms of that region, have long inter-ested scientists from the Academy and the Museum. Their most recent field work in that area includes the Belvedere Expedition of the Museum in 1962 (Lindsay, 1962) which visited 32 islands on a 43-day cruise; the Sea of Cortez Expedition of the Academy in 1964 (Lindsay, 1964; Orr, 1965), which worked the islands south of Loreto between 20 June and 4 July; and the Gulf of California Expedition in 1965 which from 9-20 August again concen-trated on the southern area. In addition the personnel of the Natural History Museum carry on continuing investigations of the biota and geology of the region near the Museum's Vermilion Sea Field Station at Bahfa de los An-geles, Baja California.