Specimens examined: Texas (Wright 416, 478, of 1851, 1852; Evans
of 1891): San Luis Potosi (Eschanzier of 1891).

The var. valida was described by Dr. Engelmann without having
seen C. scheerii, the only knowledge of that species being
obtained from the description of Prince Salm-Dyck in Cact. Hort.
Dyck., which seemed to indicate a smaller form, with fewer spines
than the Texan form. However, when visiting the collections of
Prince Salm-Dyck, Dr. Engelmann found original specimens of C.
scheerii which were exactly his var. valida. So far as
collections show the Texan form seems to be more robust than the
Mexican, but the material is too scanty to justify such a
generalization. Dr. Engelmann speaks of this species as "a
stately plant, by far the largest, of the northern Mamillariae"
Its tubercles are bright green and in beautiful contrast with the
showy yellow spines.

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