A large stout plant, simple or cespitose: tubercles large, subterete, nearly 2.5 cm. long (and about the same distance from each other): radial spines 12 to 15, stout and rigid, 18 to 30 mm. long, the lower ones the stouter, more dusky, straight or often curved downwards, the upper straight and fascicled; the solitary central spine stout, compressed, curved downwards (occasionally an additional straighter upper one), not much longer than the radials, the base nearly 2 mm. wide; all the spines horny and black-tipped; flowers 3.5 to 5 cm. long with very slender and constricted tube, saffron-yellow: fruit green seeds large (3 to 3.2 mm, long and 2 mm. in diameter), obliquely obovate and curved, smooth and brownish. (Ill. Cact. Mex. Bound. t. 74. fig. 8, seeds) Type, Schott specimens in Herb. Mo. Bot. Gard. "On grassy prairies on the south side of the Babuquibari Mountains," Sonora. Fl. July. Specimens examined: Sonora (Schott of 1853-4). Dr. Engelmann remarks that the seeds of this species are larger than those of any other Mamillaria known to him. 42. Cactus recurvatus (Engelm.) Kuntze Rev. Gen. Pl. 259 (1891). Mamillaria recurvispina Engelm. Syn. Cact. 265 (1856), not Vries. Mamillaria recurvata Engelm. Trans. St. Louis Acad. ii. 202 (1863). Globose or depressed-globose, 7.5 to 20 cm. in diameter, simple: tubercles ovate, deeply grooved, crowded, somewhat imbricate, 10 to 12 mm. long: radial spines 12 to 20, bulbous at base, compressed, rigid, recurved or flexuous, 8 to 18 mm. long, whitish or horny, interwoven with adjacent clusters; central spine solitary (sometimes an additional upper one), stouter and longer (12 to 20 mm.), dark, mostly strongly recurved and appressed (rarely straightish): flowers about 3.5 cm. long, yellow (brownish-tinged outside): fruit unknown. Type, Schott specimens in Herb. Mo. Bot. Gard. From Sonora to southern Mexico. Fl. June-August. Specimens examined: Sonora (Schott of 1855). 43. Cactus salm-dyckianus (Scheer) Kuntze. Rev. Gen. Pl. 261 (1891). Mamillaria salm-dyckiana Scheer in Salm, Cact. Hort. Dyck. 134 (1850). Subglobose: tubercles very broad and retuse, almost 2-parted by the tomentose groove, with axillary floccose wool: radial spines 7 or 8, very rigid, widely radiant, somewhat curved, 3 to 3.5 cm. long, in older tubercles 3 to 6 additional slender and straight or twisted spines; the solitary central spine very stout, erect, almost 5 cm. long: flowers and fruit unknown. Type: Scheer says that this plant, brought from Chihuahua by Potts, "unfortunately perished," and the description was drawn from fragments, which in those days were not apt to be preserved. Chihuahua. Specimens examined: Chihuahua ("Salm of 1857 "). The specimen referred to is in Herb. Mo. Bot. Gard., and reveals no additional characters; nor can the label be interpreted, except that it indicates that the specimen is from plants cultivated successfully in the gardens of Prince Salm-Dyck.