long, pitted, with subventral hilum. Type in Herb. Coulter.

San Luis Potosi.

Specimens examined: San Luis Potosi (Eschanzier of 1891).

Resembles C. grahami, but with fewer and more slender pubescent
spines, longer and less rigid central, more exserted fruit, and
much larger reddish and strongly pitted seeds with subventral
hilum.

22. Cactus tetrancistrus (Engelm.).

Mamillaria tetrancistra Engelm. Am. Jour. Sci. II. xiv. 337
(1852), in part.
Mamillaria phellosperma Engelm. Syn. Cact. 262 (1856).
Cactus pellospermus Kuntze, Rev. Gen. Pl. 261 (1891).

Ovate or ovate-cylindrical, 5 to 25 cm. high, 3.5 to 7.5 cm. in
diameter, simple or rarely branching at base: tubercles
ovate-cylindrical, 8 to 14 mm. long, with axillary
bristle-bearing wool, at length naked: radial spines 30 to 60, in
two series, the exterior bristle-like, shorter and white, the
interior stouter, longer and dusky-tipped or purplish; central
spines 3 or 4, stouter, longer, brown or blackish from a paler
base, the upper 2 or 3 (10 to 14 mm. long) straight, or one or
two or even all hooked, the lower stouter and longer (12 to 18
mm.), hooked upwards: flowers about 2.5 cm. long: fruit 1 to 2.5
cm. long: seeds large (1.2 to 1.5 mm. in diameter), globose and
wrinkled, partly immersed in a brown spongy or corky cup-shaped