In the Arizona desert region, four distinct but closely allied forms have become differentiated from the strong radiosus stock, viz.: arizonicus, deserti, alversoni, and chloranthus, all of which might be regarded as distinct species. In southeastern Texas is found an isolated form, sulcatus, occurring between the Brazos and Nueces rivers. That viviparus must be regarded as a strong northern extension of the radiosus stock can not be doubted, as the low depressed cespitose northern form seems to merge southward so gradually into the simple more robust ovate to cylindrical forms of radiosus as to suggest the propriety of regarding them all as specifically identical. The result of a closer inspection of the distribution of these nearly related forms is worthy of note. C. viviparus extends from British America and the Upper Missouri to eastern Colorado and western Kansas; neo-mexicanus (the form most nearly related to viviparus) extends from central Colorado and southern Utah into Mexico; at the southeastern edge of this range begins radiosus and extends eastward through southern Texas; from the western edge of neo-mexicanus the form arizonicus extends westward into southern California, touching chloranthus at its Utah limit, and at its California extension reaching alversoni and deserti, the latter of which extends northward into the desert region of southeastern California and adjacent Nevada. Taking this type as of Mexican origin, it seems to have entered the United States from Sonora and Chihuahua, and to have spread in three directions, viz.: eastward through southern Texas; westward and northwestward into southern California and southern, Utah; and northward to the head waters of the Missouri and British America, though we would limit the northern extension of the present specific type to central Colorado, and would regard the still more northern forms as of the same origin but entitled to specific rank. 2. ANHALONIUM Lem. Cact. Gen. Nov. (1839).