Cactus mamillaris Nutt. Gen. i. 295 (1818), not Linn. (1753). Mamillaria missouriensis Sweet, Hort. Brit. 171 (1827). Mamillaria simplex Torr. & Gray, Fl. N. Am. i. 553 (1840). Mamillaria nuttallii Engelm. Pl. Fendl. 49 (1849). Mamillaria notesteinii Britton, Bull. Torr. Bot. Club, xviii, 367 (1891). Globose, 3.5 cm. in diameter, simple or nearly so: tubercles ovate-cylindrical, 12 to 14 mm. long, slightly grooved: radial spines 13 to 17, straight, whitish, setaceous, somewhat unequal, 8 to 10 mm. long; central spine more robust, straight and porrect, puberulent, 10 to 12 mm. long, often wanting: flowers about 2.5 cm. long, yellow or reddish: stigmas 2 to 5: fruit globose, scarlet, 6 to 8 mm. in diameter: seeds globose, black and pitted, 0.8 to 1.1 mm. in diameter. (Ill. Cact. Mex. Bound. t. 74., f. 6, seeds.) Type unknown. High prairies of the Upper Missouri, from Montana to South Dakota and southward through western Nebraska to western Kansas and the eastern slopes of the mountains of Colorado. Fl. May. Specimens examined: Montana (Notestein of 1893): National Park (Tweedy 423): South Dakota, (collector unknown, in 1847, 1848, 1853): Nebraska (Hayden of 1855). 38. Cactus missouriensis similis (Engelm.). Mamillaria similis Engelm. Pl. Lindh. 246 (1845). Mamillaria nuttallii caespitosa Engelm. Syn. Cact. 265 (1856). Mamillaria missouriensis caespitosa Watson, Bibl. Index, 403 (1878). Cespitose, with 12 to 15 puberulent radial spines, the central very often wanting, larger flowers (2.5 to 5 cm. long), fruit and seeds (1.6 to 2.2 mm. in diameter), and 5 stigmas. (Ill. Cact. Mex. Bound. t. 74. f 7, seeds) Type, Lindheimer, of 1845 (?) in Herb. Mo. Bot. Gard. From the Kansas River, Kansas, and eastern Colorado, southward through Oklahoma to the San Antonio River, Texas. Specimens examined: Colorado (Greene of 1870): Kansas (Carleton 551 of 1891, from Kingman County, distributed as Mamillaria dasyacantha): Oklahoma (Carleton 120 of 1891): Texas (Lindheimer of 1845, 1850; Wright of 1850; Reverchon 725): also specimens cultivated in Goebel's Garden in 1846; and in St. Louis in 1846, 1847, 1851. The cespitose masses are often a foot broad. 39. Cactus missouriensis robustior (Engelm.). Mamillaria similis robustior Engelm. Pl. Lindh. 200 (1850). Mamillaria nuttallii robustior Engelm. and Bigel. Pacif. R. Rep. iv. 28 (1856). Mamillaria missouriensis robustior Watson, Bibl. Index, 440 (1878). Almost simple, with longer aid looser tubercles, 10 to 12 stouter radial spines (6 to 16 mm. long), a single stout central, larger flowers, and 7 or 8 stigmas. Type, Lindheimer of 1845 in Herb. Mo. Bot. Gard. From southeastern Colorado and the Canadian River (Oklahoma and Indian Territory), to the Colorado River of Texas. Specimens examined: Texas (Lindheimer of 1845, 1846; Bigelow of 1853): also specimens cultivated in St. Louis in 1847. In Bigelow's specimens the central spine is mostly lacking.