A shadow bank, such as a money-market fund, instructs its custodian bank to deposit reserves at the Fed in return for securities.
影子银行，如货币市场基金，指示其托管银行将准备金存入美联储，以换取证券。
英语百科
Custodian bank
A custodian bank, or simply custodian, is a specialized financial institution responsible for safeguarding a firm's or individual's financial assets and is not engaged in "traditional" commercial or consumer/retail banking such as mortgage or personal lending, branch banking, personal accounts, automated teller machines (ATMs) and so forth. The role of a custodian in such a case would be to: