CACTACE^ OF MEXICO SAFFORD. 563 



closely allied Mamillaria.'* At the apex of the tubercles there is a 

 more or less distinct wool-bearing areole. The flowers appear from 

 near the center of the plant, springing from the midst of a tuft of 

 wool. They are white or delicately rose tinted, with the petals 

 marked by a median stripe. The ovary and fruit are naked, the 

 seeds comparatively large and tuberculated.^ 



Among the species thus far known to science are Ariocarpus fissu- 

 ratus, sometimes called the " living rock," with the surface of the 

 tubercles grooved and warty; A. kofschuheyanus (pi. 3, fig. 4), called 

 pezufia de venado, with rose-colored flowers, and small delta-shaped 

 tubercles marked by a median longitudinal groove; A. retusus, or 

 "cobbler's thumb" (pi. 15, fig. 1), with sharp pyramidal tubercles 

 (sometimes called ^4. prismaticus) ; and A. furfuraceiis (pi. 15, fig. 2), 

 with abruptly acuminate triangular tubercles, sold for medicinal pur- 

 poses in Mexican markets under the name of " chautle." On plate 5, 

 figure 1, is shown the photograph of a plant collected by the writer 

 on the slope of the Cerro de Perote, near Parras Coahuila. It is 

 either A. fissuratus, or a new species very closely related to it. My 

 guide called it " chautle ; " but as I now picture it, lying like a gray 

 stone on the hillside of Perote, I call it " living rock." 



(^ See Thompson, C. H. Missouri Bot, Garden Rep., vol. 9. p. 128. 1S9S. 

 ^ Coulter, J. M. Contr. from U. S. Nat. Herb., vol. 3, p. 128. 1894. 



