By 1839 the fashions are starting to become what we generally associate as Victorian era styles. Small corseted waists with the large skirts and shoulders accented to look as rounded as possible.
This fashion plate also gives us a good back view of the bonnet. Notice how the ribbons used to tie the bonnet are wider? And the bit of fabric shielding the neck? These seem to be the two main style differences between Regency and Victorian bonnets.
I like the gown on the left, which do you prefer?