298 PROCEEDINGS OF THE AMERICAN ACADEMY 



very vigorous specimens more patulous : spines, when present, less 

 than 1 inch long, but stout. Flower about 2 inches in diameter, pale 

 yellow. Seed 2^ lines in diameter. It seems to be well distinguished 

 from 0. Rojinesquii (which grows only west of the Alleghanies) by the 

 smaller size, paler color, small pulvilli, usually the absence of spines, 

 the smaller flower, with all the parts less numerous, and especially 

 by the short, thick, and more or less appressed leaves. 



§ 5. Puhescentes : erectse seu procumbentes : articuli pubescentes : 

 folia minuta : aculei subnuUi. 



* FlavijlorcB. 



19. O. MiCRODASYS, Lchm. : erecto-patula ; articulis oblongis obo- 

 vatis seu orbiculatis pubescentibus Isete viridibus ; foliis minutis ; pul- 

 villis confertis inermibus lanam flavidam setasque numerosas gracilli- 

 mas flavas gerentibus. 



Only south of the lower Rio Grande, near Rinconada, etc. — Plant 

 2-4 feet high; joints 2-3 inches long, l|-2 wide; pulvilli ^-^ 

 of an inch apart. 



20. O. RUFiDA, E. in B. C. R. : erecto-patula ; articulis late-obovatis 

 seu suborbiculatis pubescentibus ; foliis longe acuminatis ; pulvillis 

 confertis setas rufidas graciles numerosissimas gerentibus inermibus ; 

 floris flavi ovario obovato pulvillis numerosis instructo ; stigmatibus 7 

 in capitulum congestis. 



Common about Presidio del Norte, on the Rio Grande : fl. May. — 

 Stem 2-4 feet high, much branched ; joints 3-6 inches long ; leaves 

 2| lines long. Flower 2| inches in diameter, with 40-50 pulvilli on 

 the ovarium. — Apparently near 0. microdasys and 0. puberula ; dis- 

 tinguished from the former by the rounded joints, larger leaves, and 

 red-brown bristles ; from the latter by the entire absence of spines, 

 and of the purplish spot which in that species surrounds the pulvillus. 

 Further investigations are necessary to decide about these closely 

 allied forms, as about most species of this intricate genus. 



* * RuhriflorcB. 



21. O. BASiLAKis, E. &. P). 1. c. : humilis ; articulis obovatis seu 

 triangularibus glaucescentibus pubescentibus e basi proliferis ; foliis 

 minutis ; pulvillis subconfertis fulvo-villosis setas gracillimas demum 

 numerosissimas fulvidas et subinde aculeolos setiformes caducos ge- 

 rentibus ; floris purpurei ovario obovato pulvillis plurimis instructo ; 



