868 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



VI. FULGIDAE. 



Joints very readily detaclied, freely falling 20. 0. fulgida. 



Joints not readily detached, persistent. 

 Spines brown or reddish, at least at base. 



Branches slender; fruit not proliferous 21. 0. spinosior. 



Branches stout; fruit proliferous 22. 0. prolifera. 



Spines white or j'ellow. 



Spines white ; petals greenish yellow, 1 cm. long or less 23. 0. alcahes. 



Spines yellow; petals red, 2 cm. long_ 24. 0. burrageana. 



„ . ^ • VII. CLAVATAE. 



Spines flattened. 



Stems very stout. 



Stems hardly clavate; ovary very prickly 25. O. invicta. 



Stems strictly clavate; ovary only slightly prickly 26. O. stanlyi. 



Stems more slender and weak 27. O. schottii. 



Spines terete, elongate, and flexible, or the central ones somewhat flattened. 



Flowers pinkish or purple 28. O. vilis. 



Flowers yellow. 



Spines comparatively short, swollen at base 29. O. bulbispina. 



Spines long and flexible, not swollen at base 30. O. grahamii. 



VIII. PUMILAE. 



Areoles (young ones) with only 1 to 3 spines 31. O. pumila. 



Areoles with 3 to 7 spines 32. 0. pubescens. 



IX. TUNAE. 



Areoles surrounded by purplish spots 33. 0. decumbens. 



Areoles not surrounded by purplish spots 34. O. d^epressa. 



X. BASIL ARES. 



Joints not pubescent 35. O. lubrica. 



Joints usually manifestly pubescent 

 Spines none or few. 



Flowers red 36. O. basilaris. 



Flowers yellow to orange. 

 Joints bright green. 



Glochids long 37. O. microdasys. 



Glochids short 38, O. macrocalyx. 



Joints grayish green 39. O. rufida. 



Spines very numerous. 



Areoles close together 40. O. pycnantha. 



Areoles distant 41. 0. comonduensis. 



XI. SETISPINAE. 



Joints elongate 42. 0. megarhiza. 



Joints obovate to orbicular. 



Flowers red or purple 43. 0. pottsii. 



Flowers yellow. 



Areoles large ; joints glaucous, purplish about areoles 44. 0. setispina. 



Areoles small ; joints green throughout 45. 0. tenuispina. 



