The ten preceding forms have evidently entered our borders from the highlands of Sonora and Chihuahua, with the exception of the Rio Grande Valley forms, texanus and sphaericus. Another species, tetrancistrus, is also a Sonoran type which has reached the eastern slopes of the mountains of southeastern California, and extended through western Arizona to southern Nevada and southern Utah, the most extended northern range of any EUMAMILLARIA. The twelfth form, goodrichii, is Lower Californian, and extends into California only in San Diego County. A summarized statement of the distribution of our twelve EUMAMILLARIA would be that two of them have extended from the low grounds of Coahuila and Chihuahua and spread along the valley of the Rio Grande; nine have come from the high grounds of Chihuahua and Sonora, four of which have extended eastward to the low levels of southeastern Texas; four have kept to the highlands west of the Pecos, and one has kept to the Colorado Valley and its tributaries, while one has a short northern extension from Lower California. The nineteen forms of CORYPHANTHA are decidedly more northern in their distribution, and are our characteristic representatives of the genus Cactus. Ten of these, however, are but northern extensions of Mexican forms, and six of the ten have simply that tongue-like northern extension in the mountains between the Pecos and the Upper Rio Grande (above. El Paso), viz.: dasyacanthus, tuberculosus, scheerii (which has also spread somewhat east of the Pecos), and the three pectinate and closely related forms radians, echinus, and scolymoides. Of the four remaining Mexican forms, macromeris is a low ground Rio Grande Valley form, extending from above El Paso well towards the Lower Rio Grande; potsii just crosses the border in the neighborhood of Laredo; and radiosus and neo-mexicanus have by far the greatest northern extension, stretching from Sonora and Chihuahua to southern Utah and central Colorado, and eastward to the Guadalupe River of Texas. The nine remaining coryphanths are distinctly forms of the United States, occupying two well-marked regions, viz.: the northern plains, and the desert region of western Arizona and adjacent California, Nevada, and Utah. In the former region is found the widespread viviparus, which extends from the southern borders of British America to the plains of eastern Colorado and western Kansas, and even crosses the Rocky Mountain divide into northern Idaho and northeastern Washington; and missouriensis, which also ranges from the high prairies of the Upper Missouri to the same southern limit, and is continued southward into Texas in its varieties similis and robustior.