41. Cactus Robustispinus (Schott) Kuntze, Rev. GEN. Pl. 261 (1891).

Mamillaria robustispina Schott in Engelm. Syn. Cact. 265 (1856).

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.