415 
Radial spines 10 to 20 mm. long. 
dasyacanthus (4), brandegei (21), mamillatus (63), alamosensis (64). 
+ + + + Radial spines more than 20. 
dasyacanthus (4), clenoides (6), mamillatus (63). 
** Central spines more than 4. 
+ Radial spines 10 or less, 
roetteri (15), roemeri (37), maritimus (40), thurbert (75). 
+ + Radial spines 10 to 15. 
Radial spines 5 to 10 mm. long. 
chloranthus (3), maritimus (40), pacificus (41). 
Radial spines 10 to 20 mm. long. 
roetterit (15), sanborgianns (26), gummosus (60), 
Radial spines more than 20 mm. long. 
roemeri (37), giganteus (67). 
+ + + Radial spines 15 to 20. 
Radial spines 5 to 10 mm. long. 
chloranthus (3), pectinatus (9), centralis (11). 
Radial spines 10 to 15 mm. long. 
dasyacanthus (4), longisetus (17), bradtianus (65), 
Radial spines more than 20 mm. long. 
giganteus (67). 
++ + + Radial spines more than 20. 
dasyacanthus (4), eruca (66). 
GEOGRAPHICAL DISTRIBUTION. 
So far as now known there are twenty-nine species of the genus 
Cereus represented within the borders of the United States, one of 
which is a West Indian form extending into Florida, and ten are pecul- 
iar to our flora. The genus is a very large and diversified one in 
Mexico, ranging in habit from small globose forms through cylindrical 
ones and climbers to the huge arborescent forms of the ‘‘cardon” for- 
ests of Sonora and Lower California. In the United States the genus 
is not represented north of the mountains of southern Wyoming or 
east of Indian Territory, except in the case of the Florida species 
referred to. As in the case of the genera already considered, our 
species appear but as outliers of the large Mexican flora. So uncertain 
is our knowledge of the latter that no attempt is made to include its 
species in this discussion. 
Omitting monoclonos, a West Indian species of KUCEREUS which 
occurs in Florida, the two great groups of the genus are represented 
in the United States by twenty-eight species, twenty-three belonging 
to ECHINOCEREUS, and five to KUCEREUS. The EKUCEREUS group is 
8898—No. 7——5 
