The modified portion of endometrium of uterus upon implantation is called decidua. It sheds when foetus is
delivered.
Decidua basalis is part underlying the chorionic vill and overlying myometrium.
Decidua parietalis ($=$ Decidua vera) is the part that lines the uterus at places other than the site of attachment of embryo.
‘Contra-deciduate’ is that animal in which even the foetal part of placenta is retained and gets absorbed to provide nourishment. Example, Talpa (male).