976 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Tubercles angled to the tip. 



Spines very unequal, some much elongate. 



Spines whitish 8. N. phymatothele. 



Spines horn-colored, reddish, or black. 

 Plants without definite central spine. 



Spines horn-colored, short, curved__9. N. magnim^amma. 



Spines reddish, long 10. N. macracantha. 



Plants with definite central spines. 



Central spines 2 11, N. johnstonii. 



Central spines solitary. 



Central spine 2 to 3 cm. long; perianth segments 



linear 12. N. melanocentra. 



Central spine 1 cm. long ; perianth segments ob- 

 long 13. N. runyonii. 



Spines nearly equal, at least none of them much elongate. 

 Flowers red to pinkish. 



Outer perianth segments ciliate 14. N". sartorii. 



Outer perianth segments not ciliate (so far as known). 

 Central spines none. 



Spines pinkish, with black tips 15. N. seitziana. 



Spines straw-colored throughout 16. N. ortegae. 



Central spines 1 or 2. 



Central sphie solitary ; radial spines nearly equal. 



17, N. meiacantha. 

 Central spines 2 ; some of tlie radials very short. 



18. N. scrippsiana. 

 Flowers yellowish. 



Central spines 4 to 6 19. N. gigantea. 



Central spines wanting 20. N. peninsularis. 



EE. Tubercles very short, symmetric. 

 Plants globose or depressed. 



Axils of tubercles naked 21. N. flavovirens. 



Axils of tubercles woolly. 



Spines partly deciduous 22. N". sempervivi. 



Spines not deciduous. 



Central spines present _-23. N. obscura. 



Central spines wanting 24. N. crocidata. 



Plants cylindric or ovoid. 

 Central spines wanting. 



Tubercles nearly terete 25. N. polythele. 



Tubercles 4-angled. 



Tubercles pointed; axils very woolly 26. N. carnea. 



Tubercles not pointed; axils not very woolly--27. N. lloydii. 

 Central spines several. 



Radial spines reduced to short bristles 28. IT. zuccariniana. 



Radial spines more elongate 29. N. formosa. 



DD. Axils of tubercles with bristles as well as wool. 

 Spines partly elongate, curved, and flexions. 



Plants without definite central spines 30. N. compressa. 



Plants with central spines. 



Central spines weak 31. N. mystax. 



Central spines stiff 32. N. petterssonii. 



