125 
“see * * Central spines more than one, and more than one of them hooked. 
Radials 8 to 12, 
wrightit (15). 
Radials 30 to 60. 
tetrancistrus (22), 
II. Tubercles with a more or less prominent groove. 
* Central spines none. 
+ Radials whitish and rigid, appressed (pectinate) and interwoven with adjacent clusters. 
Depressed-globose and simple. 
compactus (44). 
Globose and simple. 
radians (45), corniferus (47). 
Cespitose. 
pectenoides (46), sulcatus (49), 
++ Radials more slender and spreading. 
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), schecrit (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), scolymoidee (48). 
~++ Central spine erect: Mexican. 
Radials 7 or &: central 50 mm. long. 
salm-dyckianus (48). 
Radials 10 or 11: central 25 to 35 mm. long, 
maculatus (52). 
Radials 13 to 16. 
compactus (44), 
** * Central spine solitary and hooked. 
-brunneus (53), 
