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south of lat. 36°, and the country of the Gila, its large southern trib- 
utary. This has thus far furnished thirty-six Cactacee, viz. : — 
Five Mamillaria, three of them peculiar species ; - 
Six Echinocacti, none of them found elsewhere ; 
Seven Cerei, representatives of each of our four subgenera, and five 
of them peculiar ; 
Eighteen Opuntia, of which six (all peculiar) belong to the Pla- 
topunti@, two to the clavate and ten to the cylindric Cylindropuntie ; 
one of the former and nine of the latter peculiar. 
7. Tue Catirornian Recion, namely, California west of the 
Sierra Nevada, and comprising the southwestern part of the present 
State of California, produces six Cactacee, five of which are peculiar. 
They are, — 
One Mamillaria ; 
One Echinocactus ; 
One Cereus of the section Eucereus ; and 
Three Opuntia ; one of them a Platopuntia, probably only a form 
of a more eastern species, and two peculiar Cylindropuntie. 
8. Tue NortrHwestern Recion, comprising the northern parts of 
the State of California, the Territories of Utah, Oregon, and Wash- 
ington. This region has so far furnished only a single Opuntia (from 
Eastern Oregon), common also to the Missouri Region. — Mr. Geyer, 
in his account of his expedition to Oregon in 1843, mentions two 
Mamillariea and a “ Melocactus” (?), which latter he has not seen 
himself, nor are there any known specimens in existence. 
