OF ARTS AND SCIENCES. 301 



or without smaller ones, which never occurs in any form of O. Mis- 

 souriensis, where a large number of small setaceous spines is found, 

 whether larger ones are present or not. Fruit 9 lines in diameter, with 

 a small flat umbilicus. Seeds 2^ lines in diameter. 



* * Ariiculi tumidi ovati. 



25. O. ERiNACEA, E. & B. 1. c. : adscendens ; articulis ovatis seu 

 teretiusculis ; pulvillis confertissimis omnibus armatis ; aculeis 5-10 

 gracilibus rubellis, 3-5 elongatis ; bacca ovata aculeolata ; seminibus 

 magnis subregularibus. 



Near the Mojave, between the Colorado and the Californian moun- 

 tains. — Joints 2-24- inches long, 1 - It broad, and ^--f thick, some- 

 times almost cylindrical, densely covered with large white pulvilli, 

 which are only 2-3 lines apart. Spines 6-14 or even 20 lines 

 long, slender but stiff. Fruit an inch or more in length. Seeds 

 nearly 3 lines in diameter. 



26. O. ARENARiA, E. in B. C. E.. : adscendens ; articulis obovatis 

 compressis seu teretiusculis tuberculatis ; foliis minutis ; pulvillis sub- 

 confertis pallide setosis ; aculeis 1-4 robustioribus albidis fuscatis- 

 ve, cum inferioribus brevioribus 2-6 albis ; floris sulphurei ovario 

 obovato ; petalis emarginatis ; stigmatibus 5 ; bacca oblonga spinulo- 

 sa ; umbilico infundibuliformi ; seminibus magnis irregularibus. 



Sandy bottoms of the Rio Grande near El Paso : fl. May. — 

 Spreading 2-3 feet, |- - 1 foot high ; roots stout, creeping horizon- 

 tally ; joints 11-3 inches long, 1-2 inches wide, and -| - f thick, 

 more strongly tuberculated than the allied species ; leaves only a line 

 long ; pulvilli 3-5 lines apart, very bristly, especially on the old 

 joints; upper spines 9-15 lines long. Flower 2-2| inches in di- 

 ameter. Fruit about an inch long. Seeds 2^-3 lines in diameter. 

 This is the only one of our Cactacece on which the Cochenille has 

 been found. 



27. O. FRAGiLis, Haw. (Cactus fragilis, Nutt.) : subdecumbens ; 

 articulis parvis ovatis subcompressis tumidis vel subglobosis vix tu- 

 berculatis nitide viridibus ; foliis minutis ; pulvillis subconfertis magnis 

 albo-tomentosis, vix setulosis ; aculeorum 1-4 robustiorum summo 

 valido angulato fuscato porrecto, ceteris debilioribus pallidioribus pa- 

 tulis seu radiantibus ; aculeis inferioribus 2-6 gracilibus albis radi- 

 antibus ; floribus minoribus ; bacca ovata vix spinulosa, umbilico in- 

 fundibuliformi ; seminfbus paucis magnis subregularibus. 



