Nouns ending in y preceded by a vowel form their plurals by adding?

There are clear rules in transforming singular nouns to plural nouns. Below are the rules that involve words ending in y.

Nouns ending in y preceded by a vowel form their plurals by only adding-s. For example, we have the words:

boy-boys

key-keys

day-days

valley-valleys

joy-joys

However, it a noun ending in y is preceded by a consonant, the y is changed to i and - es is added. For example, we have the words:

baby-babies

lady-ladies

calamity-calamities

ceremony-ceremonies

butterfly-butterflies