Seal in the cylinder. This cylinder that is sealed in is an envelope. You just have to think back to the day, when things were more like in scroll form. So, a scroll's envelope would have been shaped like a cylinder, making this an envelope.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
We divvied up the money and put your share in the envelope.