S.S. Central America Coins

Bekko

Hello
My father passed away and left me his coin collection which consists of an 1856-S $20 AU 55 17D Full Ser, S Tilted Rt and an 1857-S $20 AU 55 20E Broken A. My question is what does the description mean?
Thank you for your help!
Becky

MsMorrisine

Ask here:

https://forums.collectors.com/categories/u-s-coin-forum