A thorny tree, with dense head and drooping branches, attaining a height of 6 meters; spines small but sharp, leaves 9.5 to 14 centimeters long, 36 to 53 millimeters broad, ovate to roundish ovate, conspicuously crenate, dark green and shining above, leathery; base acute; apex acute to obtuse, frequently emarginate; petioles 35 to 70 millimeters long, the wings 25 to 30 millimeters broad in large leaves, the average wing area somewhat less than half of the leaf blade; flowers 2 to 6, in compact axillary or terminal cymes, sometimes solitary, 14 to 20 millimeters in diameter, white, with trace of purple on the outside; calyx very small; stamens 22 to 28, free; ovary globose to oblate; locules 15 to 19; stigma almost sessile; fruit 45 to 55 millimeters long, 55 to 65 millimeters in equatorial diameter, oblate, with shallow cavity at apex, smooth, with slight longitudinal corrugations; lenticels sparse, small; oil cells usually raised; skin thin; pulp fairly juicy, sharply acid, bitter, with distinct aroma from C. histrix; juice cells short, plump, granulate, small, containing a small, greenish nucleus; seeds numerous. The limao, though rare, is not uncommon in Bohol, where it is cultivated and has also been collected by the writer in Baganga, Mindanao. The flowers appear late in April and during the early part of May, with the fruit ripening in January and February; a few fruits nearly full grown were collected in May. No. 2049 has flowered irregularly from May to December. The fruit is not eaten, but used in washing by the Boholanos and is of no economic importance. The tree is evidently quite drought resistant, and succeeds well in very scanty soil underlaid with limestone. The limao belongs in that group of the citrus fruits having free filaments, the most conspicuous characters being the compact growth of the crown, the dark-green, thick, and distinct leaves, the almost sessile stigma, and the attractive, oblate, regular-shaped fruit with its many locules, exceeding in number those in all other citrus fruits known to the writer. This species has been named in honor of Mr. E. F. Southwick, elsewhere referred to in the paper. B. A. No. 2049 (Baganga, Mindanao), 2504, 4823 (Bohol). Citrus histrix DC. Cabuyao. (Pl. Vb; fig. 1.)