Differs in its smaller size; proliferous and much more cespitose habit, the dilated base of the more spreading tubercles, fewer (8 to 12) radial spines, usually a single central spine (wanting in young plants) and somewhat larger flowers. (Ill. Cact. Mex. Bound. t. 74. fig. 1, seeds) Type, Lindheimer of 1844 in Herb. Mo. Bot. Gard. Texas, from the Brazos to the Nueces. Specimens examined: Texas (Lindheimer of 1844; Fendler 34; Wright of 1850, 1854, 1857): also specimens cultivated in St. Louis in 1845, 1848, 1853, 1859. This seems to represent the northeastern extension of the species, and doubtless it will be found merging into it south and west of the Nueces. Curiously enough one of the prominent distinctions originally given was the single central spine, while in the type specimen there occur tubercles with more than one central. 50. Cactus echinus (Engelm.) Kuntze, Rev. Gen. Pl. 260 (1891). Mamillaria echinus Engelm. Syn. Cact. 267 (1856). Globose or subconical, 3.5 to 6.5 cm. in diameter, simple: tubercles terete, conical, grooved above, 10 to 12 mm. long: radial spines 16 to 30, pectinate, straight or little curved, rigid and appressed (interwoven with neighboring clusters), ashy-white (often dusky at apex), 8 to 12 mm. long, the uppermost longer (12 to 20 mm.); central spines 3 or 4, the upper ones turned upward and intermixed with the radials, the lower one very stout, 15 mm. long, subulate from a very thick bulbous base, straight (rarely slightly curved) and porrect (deciduous in old specimens): flowers 3 to 5 cm. long: fruit oval, elongated, about 2 cm. long, green: seeds elongated-obovate. brown and smooth, about 1.8 mm. long. (Ill. Cact. Mex. Bound. t. 10) Type, the Wright and Bigelow specimens in Herb. Mo. Bot. Gard. On limestone hills, from the Pecos River, southwestern Texas, and southern New Mexico, westward to the Rio Grande (from Presidio del Norte northward). Fl. June. Specimens examined: Texas (Wright of 1849, 1851, 1852; Bigelow of 1852; Engelmann, with no number or date; Evans of 1891). The characteristic appearance of the plant is given by the very stout and straight central spine standing in each cluster perpendicular to the plant body. The range of this species, between the Pecos and the upper Rio Grande, suggests another separated group, such as is presented by C. scolymoides sulcatus to the east, between the Brazos and Nueces. Very frequently specimens of C. echinus occur in which some of the tubercles do not develop central spines, and then the spine characters resemble those of C. radians. In C. radians, also, an occasional porrect central spine is found. These intergrading forms I have only seen in Mexican material. For discussion of relationships see under C. scolymoides. ** Flowers red. + Central spine solitary or sometimes wanting. 51. Cactus dasyacanthus (Engelm.) Kuntze, Rev. Gen. Pl. 259 (1891). Mamillaria dasyacantha Engelm. Syn. Cact. 268 (1856).