MEMOIR. xx i 
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 minutiae, by 
the skilful hands of Drs. Wynian and Leidy ; and 
he kept most of the species in captivity for 
months, that he might 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 Avas 
prepared to give not only the descriptive charac- 
