Radials 10 to 17.
missouriensis* (37), similis* (38), macromeris* (64).
Radials 30 to 50, capillary.
dasyacanthus* (51).
** Central spine solitary, not hooked.
+ Central spine porrect.
Radials 6 to 17.
missouriensis* (37), robustior* (39), scheerii* (40).
Radials 30 to 50, white and capillary.
dasyacanthus* (51).
++ Central spine curved downwards.
Radials 8 to 12.
sulcatus* (49).
Radials 12 to 26.
robustispinus (41), recurvatus (42), corniferus (47),
scolymoides* (48).
+++ Central spine erect: Mexican.