1906.] NATURAL SCIENCES OF PHILADELPHIA. 177 A MONOGRAPH OF THE GENUS COLLOCALIA. BY HARRY C. OBERHOLSER. There is perhaps no other group of Swifts that equals in general interest the genus Collocalia. Some of the species build edible nests wholly or partly of saliva which is secreted in large quantities by salivary glands of unusual size; and the gathering and marketing of these nests has in some places and at some times grown to a traffic of considerable importance. Owing to the great similarity of many of the species, and the ob-scurity of the characters separating them, the group is one of the most difficult in the entire family Micropodidse. Published descriptions,^ particularly those of the older authors, are often so brief and so lacking in mention of really diagnostic characters that it is hard, sometimes even impossible, to determine with certainty the form intended. For-tunately, perhaps, the sexes, except in a very few cases, are practically identical both in size and coloration. Notwithstanding the fact that some authors have minimized the importance of difference in size, ^ The most important papers on the genus are as follows: HoRSFiELD, T., and Moore, F. — Genus Collocalia. A Catalogue of the Birds in the Museum of the Hon. East India Company, I, 1854, pp. 98-106. Bonaparte, C. L. — Note sur les Salanganes et sur leur nids. Comptes Rendus de r Academie des Sciences de Paris, XLI, 1855, pp. 976-979. Bernstein, H. A. — Beitrage zur naheren Kenntniss der Gattung Collocalia Gr. Nova Acta Academiae Leopoldinae Carolinae Naturae Curiosorum, XXVI, 1, 1857, pp. 13-32. Bernstein, H. A. — Ueber die Nester der Salanganen. Journal fur Ornithologie, 1859, pp. 111-119. Wallace, A. R. — On the Identification of the Hirundo esculenta of Linnaeus, with a Synopsis of the Described Species of Collocalia. Proceedings of the Zoological Society of London, 1863, pp. 382-385. Gray, G. R. — A Synopsis of the Species of the Genus Collocalia, with Descriptions of New Species. Annals and Magazine of Natural History, Series 3, XVII, 1866, pp. 118-128. Salvadori, T. — Osservazioni intorno ad alcune Specie del Genere Collocalia, G. R. Gr. Atti delta R. Accademia della Scienze di Torino, XV, 1879, pp. 343-350. Hartert, E. — Collocalia. Catalogue of the Birds in the British Museum, XVI, 1892, pp. 496-511. Hartert, E.— Gen. Collocalia G. R. Gray. Das Tierreich, I, 1897, pp. 66-70. 12
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