58 EXPLANATION OF THE PLATES. 
Roetter of St. Louis, under the personal superintendence of Dr. Engelmann. The drawings 
made on the spot by Mr. H. B. Méllhausen, the artist of the expedition, greatly aided the work 
and were made use of, and even partly copied, especially in the plates exhibiting the Cylindric 
Opuntiz. LAS fhe 
