sur·plice [súrpləss](plural sur·plic·es)
|ecclesiastical garment: a white ecclesiastical outer garment like a smock, with wide, often flared sleeves, and varying in length|
[13th century. Via Anglo-Norman surpliz < medieval Latin superpellicium "(vestment worn) over a fur garment" < pellicium "fur coat"]
In this case the surplices stand for the underworlds armor and is black instead of white.