It seems best to keep this northwestern form specifically
separate from that large assemblage of southern forms that have
been commonly referred to it. The forms referred to this species
from western Kansas (Smyth's check list) have not been examined,
and they may represent intermediate forms, inclining to simple
habit and ovate form, as in the Colorado forms. The southern
type (C. radiosus) is distinguished from C. viviparus not only by
its very different range, but also by its ovate to cylindrical
form, simple habit, more numerous (12 to 40) and longer (6 to 22
mm.) radial spines, usually more numerous (3 to 14) central
spines in which the upper are more robust than the lower, porrect
lower central, obtuse stigmas, and brown obovate straight seeds.

58. Cactus radiosus (Engelm.).

Mamillaria vivipara Engelm. Pl. Fendl. 49 (1849), not Haw.
(1819).
Mamillaria radiosa Engelm. Pl. Lindh. 196 (1850).
Mamillaria vivipara radiosa texana Engelm. Syn. Cact. 269
(1856).

Ovate or cylindrical, 5 to 12.5 cm. high and about 5 cm. in
diameter, simple or sparingly proliferous: tubercles terete, more
or less grooved above, 8 to 12 mm. long: radial spines 20 to 30,
straight, slender, with with dusky apex, very unequal, 6 to 8 mm
long; central spines 4 or 5, stouter, yellowish or tawny, 8 to 12
mm. long, the upper ones the longer and more robust, the lowest
one shorter and porrect: flowers 3.5 to 5.5 cm. long, about the
same diameter when fully open, violet to dark purple: stigmas 7