Specimens examined: Coahuila (Palmer 378 of 1882; Pringle 3117 of 1890): Nuevo Leon (Wislizenus of 1847): San Luis Potosi (Poselger of 1851; Eschanzier of 1891). 55. Cactus potsii (Scheer) Kuntze, Rev. Gen. Pl. 261 (1891). Mamillaria potsii Scheer in Salm Cact. Hort. Dyck. 104 (1850). Cylindrical, 30 to 35 cm. high, 2.5 to 3 cm. in diameter, somewhat branching: tubercles ovate, obtuse, very lightly sulcate, with somewhat woolly axils: radial spines very numerous (entirely covering the whole plant), slender and white; central spines 6 to 12, stouter from a broad base: flowers large, green, or reddish: fruit red. Type unknown. From the Rio Grande region, near Laredo, Texas, to Chihuahua. Specimens examined: Texas (Poselger of 1851): Chihuahua (specimens from Coll. Salm-Dyck.). 56. Cactus tuberculosus (Engelm.) Kuntze, Rev. Gen. Pl. 261 (1891). Mamillaria strobiliformis Scheer in Salm Cact. Hort. Dyck. 104 (1850), not Muhlenpf. (1848), nor Engelm. (1848). Mamillaria tuberculosa Engelm. Syn. Cact. 268 (1856). Ovate to cylindrical, 5 to 15 cm. high, 2.5 to 5 cm. in diameter, simple or branching at base: tubercles short-ovate from a broad base, 5 to 6 mm. long, deeply grooved, crowded and imbricate, at length covering the older parts as naked and gray corky protuberances: radial spines 20 to 30, slender but stiff, white, radiant and interwoven with adjacent clusters, 4 to 8 mm. long (uppermost rarely 10 to 12 mm.); central spines 5 to 9, stouter, purplish above, the upper ones longer, erect, 10 to 14 mm. long (sometimes even 16 to 18 mm.), the lower one shorter (6 to 8 mm.), stout, porrect or deflexed: flowers about 2.5 cm. in diameter, pale purple: fruit oval, elongated (sometimes almost cylindric), red, about 18 mm. long: seeds subglobose, brown and pitted, very small (0.8 to 1.2 mm. long). (Ill. Cact. Mex. Bound. t. 12. figs. 1-16) Type of Scheer's strobiliformis is unknown; but the specimens of Prince Salm-Dyck in Herb. Mo. Bot. Gard. are marked "authentic" by Dr. Engelmann. The Wright specimens in the same Herb, represent the type of M tuberculosa Engelm. From the mountains of extreme southwestern Texas (common west of Devil's River), southward into Chihuahua and Coahuila. Fl. May-June. Specimens examined: Texas (Wright 18, 19, 20, 23, 24, 29, 30,31,32, 535, of 1849 and 1852; Bigelow of 1852; Engelmann, with no number or date; Evans of 1891): Chihuahua (Pringle 250, 251 in part, and 258 of 1885): Coahuila (Palmer of 1880): also specimens from Coll. Salm. Dyck in 1857; also growing in Mo Bot. Gard. 1893 (specimens, sent by G. G. Briggs in 1892 from El Paso, Texas.