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11. M. pectinataEng. Simple, globose, 2.5 to 6.5 cm. in diameter: lower tubercles 
short conical, 4 to 6 mm. long, the uppermost flower-bearing ones terete, longer, sul- 
cate, 10 to 12 mm. long: areolie oblor g: spines all radiating, 16 to 74, rigid, recurved, 
about equal, 6 to 10 mm. long, horny or white, those on the uppermost tubercles with 
the upper ones fascicled and longer, 12 to 18 mm. long: flowers 5 to 7.5 em. in diam- 
eter.—On the Pecos. 
12. M. Bchinus Eng. Simple, globose, 3.5 to 6.5 cm. in diameter: tubercles round- 
conical, 10 to 12 mm. long: areolw orbicular: spines straight or a little curved, white; 
radial ones 16 to 30, 8 to 12 mm. long, the uppermost a little longer, 12 to 20 mm, long ; 
central ones 3 or 4, the lower one very stout, subulate from a very thick base and 
perpendicular to the center of the plant, the upper ones erect as are the radial: 
flowers large, about 3.5 to 5 em. long.—On the Pecos. “A very striking plant, char- 
acterized by the unusually stout and subulate lower central spine, which, together 
with the globular shape, gives it the appearance of some echinoid” (Lngelmann). 
13. M. scolymoides Scheidw. Nearly simple, globose or ovate, 5 to 7.5 em. high: 
tubercles conical, 10 to 16 mm, long, the upper elongated, incurved, imbricate: radial 
spines 14 to 20, straight or often recurved, white or horny, 10 to 20 mm. long ; central 
ones 1 to 4, darker, longer, 18 to 32 mm. long, the upper ones turned back with the’ 
radials, the lower stouter, longer and bent downwards: flowers 5 cm, long.—On the 
Pecos. 
14. M. calcarata Eng. Globose, proliferous, cespitose, larger heads 5 to 6.5 cm, in 
diameter, the cespitose masses a foot or more large: tubercles ovate-conical from a 
dilated base, spreading (or in older flowering plants often somewhat appressed and 
imbrieate), 14 to 18 mm. long: spines white, 8 to 16 mm. long; radial ones 8 to 12, 
rigid, subulate, straight or a little recurved ; single central one stouter, subulate, 
recurved (wanting in younger plants); 3 to 5 fascicles of more slender adventitious 
spines often occuring in addition from the top of the areola: flowers large, 5 to 6.5 
em. long and broad, sulphur yellow and reddish at base within.—From the Brazos 
to the Nueces. 
+ + Flowers red or reddish: sepals fimbriate. 
15. M. Pottsii Scheer. Cylindrical and somewhat branching: tubercles ovate, 
obtuse, slightly suleate, with somewhat woolly axils: radial spines very numerous, 
slender, white; central ones 6 to 12, stouter, from an enlarged base, nodulose: flowers 
large: berries rose-color.—On the Rio Graude below Laredo. 
16. M. strobiliformis Scheer. Ovate or ovate-cylindrical, simple or sparingly 
proliferous at base, 5 to 12.5 em. high: tubercles ovate from a rhomboidal base, short, 
obtuse, deeply grooved, in age losing the spines and covering the lower part of the plant 
like corky protuberances, with very villous axils: outer spines 20 to 30, rigid, white, 
4 to 8 (rarely 10 to 12) 1am. long ; inner ones 5 to 9, stouter, 8 to 18 mm. long, grayish- 
purple, the upper ones longer and erect, the lowest one shorter, stout, perpendicular 
or deflexed ; interior spines of the upper tubercles forming a tuft of grayish-purple 
color on top of the plant: flowers central on the very densely tomentose summit, 
2.5 em. in diameter, very pale purple: berry red, 18 mm. long, 6 mm. thick. (AM. 
tuberculosa Eng.)—Common from the San Pedro to El Paso.“ The short corky tuber- 
cles, with very.deep grooves, and very woolly when young, together with the long 
red fruit, distinguish this species from all the allied forms ” (Engelmann). 
17. M. dasyacantha Eng. Simple, nearly globose, 3.5 to 6.5 cm. high: tubercles 
terete, loosely arranged, slightly grooved, 8 to 10 mm. long, with somewhat villous 
axils: spines straight, more slender and soft than usual (often capillary), spreading 
but not radiating, 12 to 24 mm. long, the exterior 25 to 35 white, the interior 7 to 13 
dusky-purple and longer; central spine single, erect, often wanting: berry central, 
ovate.—Eagle Pass to El Paso. 
18. M. vivipara Haw. Simple or cespitose, 2.5 to 12.5 cm. high: tubercles terete, 
loosely arranged, slightly grooved, 8 to 12 mm. long: spines straight, rigid; the ex- 
terior widely radiate, white, 12 to 36, 6 to 20 mm. long; the central 3 to 12, stouter, 
