In chains

I've been noticing this headstone for some time now on my regular drives to Winchester and today curiosity finally got the better of me and I stopped off to have a look at it. From the road all you can see is the top of a headstone with chains draped over it. I hadn't guessed it was an anchor. Buried beneath it is John Seymour William Talbot Ponsonby, a Lieutenant in the Royal Navy who died in 1895 aged 25, along with his sister Evelyn Mary Georgiana who died in 1915, aged 39 (if my maths is correct).