Dr. Engelmann regarded this species as possibly only a variety
of C. heyderi, to which it is certainly very closely allied
through var. hemisphaerica, but the different tubercles and
fewer stouter spines serve so well to distinguish it that it
seems best to retain its specific rank.

In reference to the citation of the original description an
explanation seems necessary, which will apply to numerous similar
cases. The Pacif. R. Rep. iv. 27 (1856), Syn. Cact. 263
(1858), and Cact. Mex. Bound. 9 (1859), have each been cited
as the original publication. The confusion has arisen from the
fact that in both the publications of 1856 the description in the
Rep. Mex. Bound. is referred to, and in that report the plant
is fully described as "sp. nov." However, the publication of
the Boundary Report was long delayed on account of the
preparation of the plates, and in the meantime both the
publications of 1856 had appeared, in each one of which the
species is distinctly characterized and reference made to the
description in the forthcoming Boundary Report. As between the
two publications of 1856 the Syn. Cact. (Proc. Amer. Acad.
iii. 259) was evidently distributed first.

8.Cactus gummiferus (Engelm.) Kuntze. Rev. Gen. Pl. 260
(1891).

Mamillaria gummifera Engelm. Wisliz. Rep. 21 (1848).

Hemispherical, 7.5 to 12.5 cm. broad and 6 to 10 cm. high:
tubercles 12 to 15 mm. long: radial spines 10 to 12, the lower