Specimens examined: Texas (Wright 227 of 1849, also of 1852; Nealley of 1892): Coahuila (Bigelow of 1853): Chihuahua (Pringle 212): also growing in Mo. Bot. Gard. 1893. The plants densely covered above with delicate ashy-gray spines and with naked tuberculate base are readily recognized. It still remains an open question whether the flowers are developed from the axils of tubercles of the same season or the last ones of the preceding season. Dr. Engelmann inclined to the latter view, as all the other characters of the plant associate it with the "lateral-flowered" species; and in the absence of definite observation we have retained it there. If the nearly central flowers indicate that they are produced from growth of the same season the species would seem to be allied to Coryphantha, in which group its small flowers and small tubercles would be anomalous. 13. Cactus micromeris greggii (Engelm.). Mamillaria micromeris greggii Engelm. Syn. Cact. 261 (1856). Larger (2.5 to 5 cm. in diameter) and becoming oblong, with larger globose-ovate tubercles (2 to 2.5 mm. long), fewer rigid spines all radiant (interior 5 to 7 shorter and stouter, 1 to 2 mm. long; the outer 15 to 18, 3 to 4 mm. long), and fruit 1.5 to 2 mm. long. (Ill. Cact. Mex. Bound. t. 2. figs. 5-8) Type, Gregg 508 in Herb. Mo. Bot. Gard. Mountain ridges near Saltillo, Coahuila. Said by Budd to occur within the southern borders of Pecos County, Tex. Specimens examined: Coahuila (Gregg 508; Palmer of 1880). It is a question whether this variety does not merely represent an older and better developed plant than those upon which the species is based. Mr. Harry I. Budd, who has made extensive collections of Texan and Mexican Cacti for the market, reports that it is impossible to separate sharply the variety from the species in the field, and regards the difference merely as one of age. Unfortunately, only living material of the species could be examined, but its characters seem well sustained even in the most vigorous plants, some of which reach the size of the variety. Through this variety the species is brought very near the following: 14. Cactus bispinus. Mamillaria microthele Muhlenpf. Allg. Gart. Zeit. p. 11 (1848), not Lem. (1838). Differs from the last form (var. greggii) chiefly in its cespitose habit, much larger tubercles, and two unusually stout and short central spines (fide Engelmann, who examined specimens in Coll. Salm-Dyck). Credited to Mexico in general, but said by Budd to occur within the southern border of Pecos County, Tex. ** Central spines present and one or more hooked. + Mostly globose and simple plants (occasionally somewhat cylindrical). 15. Cactus wrightii (Engelm.) Kuntze. Rev. Gen. Pl. 261 (1891). Mamillaria wrightii Engelm. Syn. Cact. 262 (1856).