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before explored ; and Dr. Bigelow, the botanist and physician of Cap- 
tain A. W. Whipple’s expedition along the 35th parallel, availed him- 
self of these opportunities in a most successful manner; while Dr. 
F. V. Hayden, almost unaided in his adventurous expedition, has ex- 
' tended our knowledge of the northernmost Cactacez in the regions of 
the Upper Missouri and Yellowstone Rivers. 
The last, but by no means least addition, was made in 1854 and 
1855, by Mr. Arthur Schott, during the exploration under Major 
Emory of the country south of the Gila River, known as the Gads- 
den Purchase. 
Most of the materials brought together by these different explorers 
have come into the hands of the writer ; but few of the discoveries 
made since 1847 and 1848 have been given to the public ;— partly 
because the material on hand very often was incomplete, and partly 
because it seemed desirable to publish the whole in an elaborate form 
with the Reports of the Boundary Commission and those of the Pacific 
_ Railroad Surveys. These reports are now in preparation; but the 
splendid plates which are to illustrate the natural history of these 
plants cannot be finished for some time ; it is therefore deemed ad- 
visable now to publish short descriptions of the new species, and sys- 
tematically to arrange them with those before known. 
CACTACE. 
Tribus I. TUBULOSA, Miquel. 
Subtrib. 1. Parattetz. Cotyledones margine hilum versus spec- 
tantes, lateribus seminis parallelz. 
I. MAMILLARIA, Haw. 
Ovarium baccaque leves. Semina fere exalbuminosa. Cotyledones 
abbreviate, plerumque erect, subconnate. — Plante maumillato-tu- 
berculatz ; inflorescentia laterali s. verticali. 
Subgen. 1. Evmamitiania. Flores ex axillis tuberculorum anni 
prioris nunquam sulcatorum: ovarium plerumque immersum versus 
fructus maturitatem emergens. 
. § 1. Polyacanthe, Salm. 
1. M. micromeris, E. in Bound. Comm. Rep.: parvula, simplex, 
globosa ; tuberculis minimis verruceformibus confertissimis ; areolis 
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