380 
+ + + + + Central spines 5 to 7. 
Radials 3. 
pilosus (17). 
Radials 7 to 9. 
pringlei (18). 
Radials 21. 
unguispinus (44). 
tee + + + Central spines 8 to 10. 
Radials 10 to 14. 
octocentrus (43). 
Radials 16 to 30. 
simpsoni (50), minor (51), robustior (52). 
** * Spines entirely wanting. 
myriostigma (7). 
GEOGRAPHICAL DISTRIBUTION. 
The genus Echinocactus has a strong development within the United 
States, but has no such northern extension as Cactus, its extreme north- 
ern limit being in the southern borders of Colorado, Utah, and Nevada, 
unless we except the possible occurrence of 7. simpsoni robustior in 
Washington. With more careful exploration, especially of the Great 
Basin region, other forms will be discovered, but as recognized in this 
revision, 86 are known within our borders, 15 of which are restricted to 
the United States. Owing to the insufficiency of knowledge no state- 
ment can be made concerning the distribution of Mexican forms, and 
nothing very satisfactory concerning those occurring within the United 
States. 
No Hehinocactus has such an east and west distribution along our 
borders as have some species of the genus Cactus, the only one approach- 
ing any such distribution being cylindraceus, which seems to be a Lower 
Californian form that has extended from southeastern California to 
southern Utah and southwestern Texas, although it may have an 
equally wide Mexican distribution. All the other species seem to have 
extended northward along comparatively narrow lines, and indicate in 
a general way their Mexican origin. Other Lower Californian forms 
which extend within our boundaries are: peninsula, which only reaches 
the southern borders of California; and emoryit and lecontei, which are 
also Sonoran, the former ranging northward in the lower basin of the 
Colorado (extreme southeastern California and adjacent southwestern 
Arizona), the latter extending farther northward to southern Nevada 
and southern Utah. The occurrence of forms in Lower California which 
seem best referred to wislizent is somewhat puzzling, as otherwise 
that species has been found restricted to a much more eastern distribu- 
tion, one of Chihuahuan origin. The only pure Sonoran form that 
reaches us, so far as recorded, is polycephalus, which extends northward 
through the lower basin of the Colorado to southern Nevada and 
southern Utah, an extension resembling that of lecontei. Types from 
Chihuahua and Coahuila have extended into Texas, usually ranging 
