Pupa

Just before the skin is dropped, a black appendage at the end of the abdomen with barbed hooks on the tip is twisted into the silk pad.  This post is called a cremaster and must get firmly hooked into the silk or the pupa will fall and die.  The soft green casing changes shape and the yellow stripes move upwards to form a line of golden dots.  This pupal casing or shell hardens and is called a chrysalis. 

Since the only silk made was used to attach the chrysalis, not to make a silken covering, it is incorrect to call it a cocoon.  Most moth caterpillars, but not all, will spin a silk cocoon to protect them while they pupate.  If you find a cocoon - a butterfly will never come out of it - only a moth.