MEMOIR. xxi 



The great work, however, to which he chiefly 

 devoted himself, was the one which follows, being 

 an amplification of his Monograph on the Ter- 

 restrial Mollusks of the United States. It was 

 his intention to publish something that, in com- 

 pleteness and in the style of its mechanical ex- 

 ecution, should be unsurpassed by any similar 

 work. He therefore spared no pains and no 

 expense to render it as perfect as possible. He 

 obtained characteristic and living shells of every 

 species and variety ; he procured the best artists 

 to figure and engrave both the animal and the 

 shell J many of which were repeatedly drawn or 

 engraved before he was quite satisfied with the 

 result; — he had thorough and accurate dissec- 

 tions made of all their anatomical minutise, by 

 the skilful hands of Drs. Wyman and Leidy ; and 

 he kept most of the species in captivity for 

 months, that he niight be able to observe their 

 habits, the variations they exhibited, and the 

 changes they underwent by age, food, etc. To 

 carry out fully his design, he employed an expe- 

 rienced collector to spend one winter in Florida 

 and the adjacent Keys, and another in the South- 

 western States, including Texas ; and thus he was 

 prepared to give not only the descriptive charac- 



