In 1873 Eustace married Maria Adelaida MOREY ARIAS in Ambato, Peru. On the register his surname (as written by the priest) looks like SENIOR. However, a document written (in Spanish) supporting his wish to marry has a surname which looks like SERREL. This states that he comes from Kingston upon Thames, and is Eustace Michael Meljado (?) Serrel, single, the legitimate son of Eustace and Lady Jane.
I can't find a likely birth in Surrey on FreeBMD. Could some kind person see if he or his family are on a census? (1861 would be the best bet)
Many thanks
Philip