VMS Help TCPIP Services, Programming Interfaces, RPC XDR Routines, xdr_opaque, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 xdrs
    A pointer to an XDR stream handle created by one of the XDR
    stream handle creation routines.
 op
    A pointer to the opaque data.
 cnt
    The size of op in bytes.