980 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Central spines yellow. 



Central spines glabrous 99. N. pygmaea. 



Central spines pubescent. 



Flowers white ^ 100. N. wildii. 



Flowers yellowish 101. N. seideliana. 



Central spines red to brown. 

 Outer perianth segments ciliate. 



Central spines shorter than the flower ; perianth segments 



acute 102. N. barbata. 



Central spines longer than the flower; perianth segments 



obtuse 103. N. mercadensis. 



Outer perianth segments entire. 

 Axils of tubercles setose. 



Inner perianth segments white to yellowish. 

 Central spines 3 or 4. 



Radial spines about 25 ; flowers 2 cm. long. 



104. N. kunzeana. 

 Radial spines about 20 ; flowers 1 cm. long. 



105. N. hirsuta. 



Central spines 7 to 9 106. N. multihamata. 



Inner periantli segments red or reddish. 

 Radial spines weak and hairlike. 



Central spines several 107. N. longicoma. 



Central spines solitary 108. N. bocasana. 



Radial spines stiff. 



Radial spines glabrous 109. N. multiformis. 



Radial spines pubescent 110. N. scheidweileriana. 



Axils of tubercles not setose. 

 Flowers 2.2 cm. long or more. 



Central spines solitary 111. N. saffordii. 



Central spines 3 112. N. schelhasei. 



Flowers 1 to 1.5 cm. long. 



Plants cespitose 113. N. glochidiata. 



Plants solitary. 

 Inner perianrh segments acuminate. 



114. N. trichacantha. 

 Inner perianth segments merely acute. 



115. N. painteri. 

 FF. Plants stout ; at least the central spines stout-acicular to subu- 

 late. 

 Outer perianth segments ciliate. 



Perianth rotate; stigma lobes red 116. N. mainae. 



Perianth campanulate ; stigma lobes green. 



Flowers white 117. N. boedekeriana. 



Flowers purple to pinkish. 



Radial spines often as many as 30 118. W. microcarpa. 



Radial spines often as few as 12 119. N. sheldonii. 



Outer perianth segments not ciliate. 

 Bristles (sometimes only one, sometimes many) present in axils 

 of the tubercles. 



