16 



In limestone formation at 4000 feet altitude, about 4 miles 

 south of Marathon, Brewster County, Texas. 

 Named for Mrs. Nellie Davis, wife of the collector of the type 

 specimen.- — Early spring- — Type specimen in the Herbarium of 

 the New York Botanical Garden. 



This Cactus is found in a restricted area on the slopes of 

 high hills in gravelly soil, living in places where a temperature as 

 low as 28 degrees is sometimes recorded for short periods of 

 time. It blossoms late in years of drought. No specimens have 

 been collected so far that form more than six heads. 



New York, N. Y. 



