* Central spines none.
Radials 5 to 9, stout.
meiacanthus* (7).
Radials 20 to 40.
micromeris* (12), greggii (13).
Radials 40 to 80.
lasiacanthus* (10), denudatus* (11).
** Central spine solitary and not hooked.
+ Central spine longer than the radials.
Radials 7 or 8: tubercles very long (40 to 50 mm.).
longimamma (36).
Radials 15 to 20: tubercles 6 to 8 mm. long.
eschanzieri (21).
++ Central spine shorter than the radials.
Radials 5 to 9, stout.
meiacanthus* (7).
Radials 9 to 22.
heyderi* (5), hemisphaericus* (6), gummiferus (8), gabbii
(34),
sphaericus (35).
*** Central spine solitary and hooked.
+ Stems slender cylindric: Lower Californian.
Centrals 1, 20 to 30 mm. long.
roseanus (23).
Centrals 1 to 4, 20 to 50 mm. long.
setispinus (24).
++ Stems depressed-globose to ovate.
Radials 4 to 6, rigid.
uncinatus (9).
Radials 8 to 12.
wrightii* (15).
Radials 15 to 30.
grahami* (19), eschanzieri (21).
Radials 50 to 60.
barbatus (18).
**** Central spines more than one, and none of them hooked.
+ Slender or sometimes stout cylindrical plants, branching at
base: Lower Californian.
brandegei (3), setispinus (24), halei (25).
++ Depressed-globose to ovate and stout cylindrical.
++ Radials few (3 to 12) and rigid: Mexican.
Radials 3: centrals 3.
alternatus (1)
Radials 7 or 8: tubercles 40 to 50 mm. long.
longimamma (36).
Radials 10 to 12: tubercles 12 to 15 mm. long.
gummiferus (8).
++++ Radials numerous (16 to 60), capillary or bristle-like.
Radials 15 to 30, slender but rigid (bristly).
acanthophlegmus(2), densispinus (4), bispinus (14),
rhodanthus (26), sulphureospinus (27), palmeri (29),
pringlei (32).
Radials 30 to 60 or more, mostly capillary.
tetrancistrus* (22), capillaris (28), texanus* (31),
spaerotrichus (33).
***** Central spines more than one and but one of them hooked.
Radials 10 to 15.
goodrichii* (16), setispinus (24).
Radials 15 to 30.
pondii (17), grahami* (19), bocasanus (20).
Radials 30 to 60.
tetrancistrus (22).
****** Central spines more than one, and more then one of them
hooked.
Radials 8 to 12.
wrightii* (15).
Radials 30 to 60.
tetrancistrus (22).