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 xo6 THE CONDOR [ VoL VII been visited once only by an ornithologist since I867, a that once being by Mr. C. H. Townsend in I889, b at which time a limited period only was spent on the islands and the meagre knowledge ot the avifauna that was obtained, important as it was, served only to whet the interest of all western ornithologists. Since i897 several expeditions have touched at these islands en route to and from the Galap- agos group, and one expedition was sent to Los Revillagigedos by the California Academy of Sciences in 9o3. This party spent several months in the region, principally upon Socorro Island, and the report of their work, when published, will undoubtedly add much to the history of the group. Most of the islands along the coast-line of Lower California were at one time an integral part of the mainland. San Martin Island, however, is undoubtedly of volcanic origin and of comparatively recent eruption, the lava blocks being sha[p and clean-cut on the edges. Guadalupe also is of volcanic origin but is older than San Martin, the lava on Guadalupe being well weather-worn. Cerros Island, while at one time part of the mainland, shows traces of volcanic disruption in the torsion of the strata, but no direct eruptive evidences were seen. Socorro and San 'Bn'edicte Islands, however,' are'strikingly volcanic, the former' being in reality an active volcano, while San Benedicte is a vast heap of broken lava, pumice, ashes and obsidian. San Benedicte has but little vegetation, that little being main- ly grasses, but on Socorro soil has formed and the island is a dense growth of cac- tus, grasses, vines, shrubs and even large trees; this,. taken together with the ex- tensive and peculiar avifhun'a, shows the great age of Socorro as compared with San Benedicte. Clarion Island, also, owes its origin to volcanic sources and to the sub- sequent action of the corals which have surrounded the island with reefs. The vegetation on Clarion is dense and consists principally of cactus; on some portions of the island a tree (Dodonava viscosa L.) is abundant, and it is on the tops of these trees that the boobies (Xula pDcatrivd wbsteri) nest by thousands. These trees are und,ergrown by and 'interlaced with a network of thorny creepers (Cesalpznza bon- iluce'lla R0xb.) peculiarly iough arid lingihg' and ihese'crefi"per, s"aid the cactus in m'akng ocomotmn mposslble wffhout the aid of a machete to cut a path. These thorn ree,/)ers: are also a 'ource of great danger t.o 'the bdobie liesking Over them, for if a booby inisegalighting on the nest wtien ;:i('turning hea3y ladeh with or if ir/'riSing the heavy brd falters and drops, the thorny 'ropes siize him in' a grasp'that never relaxes; to this we' found many a skeleton bearing grim'testimony. The writer regrets exceedingly. that lack of time and space prevent his giving 't6 this list the detail it warrants.' Much might be written on the curious habits of these little-known species, especially on the breeding habits, many nests and eggs having been found, and of species whose nesting habits were and are unknown to the majority of workers. C01ymbus nigricolliscalif0rnicus (H:.). We saw one individual of this species on San Geronimo Island on March x7th;  it is reported commonly, from the coast of Lower California in winter. Cer0rhincha m0n0cerata (Px..). Rhinoceros Anklet. A single specimen was taken near San Geronimo Island about March 9th, [899. Ptych0ramphus aleuticus (Pxx. x..). Cassin Anklet. This species is common on all the islands as far south as Ascuncion Island, becoming abundant on San Geronimo, San Benitos and Natividad Islands, less common on Todos Santos, San Martin, San Roque, Ascuncion and Cerros Islands; this is probably the most abund- a. CJ[ Grayson, Col. A, J., Exploring Expedition to the Island of Sototto. Proc. Bost. Soc. Nat. Hist., XIV, 87o-7 r, 87-e89. : b. Cf Townsend, C. H., Birds from lhe Coast of Western North America and Islands. etc. Proc. U.S. Nat. Mus. XIII, 189o. 131-142.