Mamillaria prismatica Lem. Hort. Univ. i. 231 (1839).
Cactus prismaticus Kuntze, Rev. Gen. Pl. 261 (1891).
Flat above, top-shaped below, 7.5 to 12.5 cm. in diameter:
tubercles (upper portion) close]y imbricate but squarrose-
spreading, sharply triangular-pyramidal and very acute (with a
sharp cartilaginous tip, which usually disappears with age and
leaves the older tubercles blunt or retuse), 18 to 25 mm. long
and about as wide at base, the upper surface almost plane and
smooth, except that it is more or less pulverulent and usually
bears a small tomentose pulvillus (often evanescent later) just
behind the claw-like tip: flowers rose-color: fruit elongated-
oval and reddish. (Ill. Lem. Cact. t. 1.) Type unknown.
Referred to Mexico in general, but reported definitely only from
San Luis Potosi. Undoubtedly found in Coahuila, and possibly
crosses the Rio Grande in the region of the "Great Bend."
Specimens examined: San Luis Potosi (Eschanzier of 1891): Mexico
in general (specimens from Coll. Salm-Dyck in 1858; Schott of
1858): also specimens cultivated in Mo. Bot. Gard. in 1881; also
growing in same garden in 1893.