OF ARTS AND SCIENCES. 263 



brevi-ovatis axilla lanata setigeris ; aculeis radiantibus 11-15 albidis, 

 centralibus 3-4 fusco-atris, inferiore paulo longiore deorsum unci- 

 nate ; floribus lateralibus. 



San Diego, California. — Two or three inches high. Radial 

 spines 2-|- - 3| lines long ; the lower central spine a little longer. 

 Flowers apparently yellowish-white, and half an inch in diameter. 



§ 3. Setosce, Salm. 



9. M. BicoLOR, Lehm. : depressa, ovata, s. cylindracea, prolifera ; 

 axillis lanatis ; tuberculis parvulis conicis ; aculeis exterioribus 16-20 

 tenuissimis recurvato-radiantibus, centralibus 2-4 rigidis, majoribus 

 albis apice nigris interdum subpollicaribus, supremo plerumque longis- 

 simo incurvo ; floribus parvulis purpureis ; stigmatibus 5. 



Abundant on the calcareous hills of the Rio Grande below Laredo, 

 Texas, Dr. Poselger: fl. June and July. — Plant 3-12 inches high, 

 the larger specimens 2-3 inches in diameter ; radial spines 1-2, 

 lower central ones 4-5, the upper 6-10 lines long. Flower about 

 9 lines long. 



§ 4. Ce7itrispincs, Salm. (All our species are simple and 



have a milky juice.) 



10. M. Heyderi, Muhlenpf. (1848): simplex, depresso-globosa ; 

 tuberculis elongatis pyramidatis subquadrangulatis ; aculeis radianti- 

 bus 10 - 20 rectis, inferioribus longioribus, central! singulo breviore ; 

 floribus lateralibus sordide rubellis ; baccis elongato-clavatis ; semini- 

 bus parvis rugulosis fulvis. 



Var. a. APPLANATA (M. applanata, E. in PL Lindh. 1850) : vertice 

 applanato s. depresso, aculeis radialibus 15-22. 



Var. /3. HEBiispHiERiGA (M. hemisphserica, E. I. c.) : vertice con- 

 vexo, aculeis radialibus 9 - 12. 



From San Antonio and New Braunfels, Texas, to Matamoras and 

 westward to El Paso : fl. April, May. — Var. a. is the Northern and 

 Western, and ^. the Southern form. — M. decUvis, Dietr. seems to 

 belong here ; but I have never met with a description of this plant. 



11. M. BIEIACANTHA, E. in B. C. R. : hemisphserica ; tuberculis quad- 

 rangulato-pyramidatis compressis ; aculeis paucis (5-9) rigidis rectis 

 s. recurvatis, inferioribus paulo longioribus, centrali singulo erecto s. 

 sursum flexo et cum ceeteris radiante ; floribus et baccis prsecedentis. 



Western Texas and New Mexico. — Very similar to the last ; but 

 tubercles larger, more compressed, more loosely arranged ; the spines 

 fewer and stouter ; perhaps only a variety of it. 



