Well Kath and Tracy, thanks for asking a very interesting question. In fact, this is one of those questions that is hard to answer definitively as usage is changing.

Most current guides to British English punctuation state that after names which end in s, you add an apostrophe and an s.

e.g. Jones's book - Jones' would end s + apostrophe s

However, names from the ancient world are often written with just an apostrophe

e.g. Achilles' anger - the ending would be s + apostrophe

It is also customary to make an exception for names that end with an 'iz' sound.

e.g. Moses' leadership. Moses' would end s + apostrophe
And Wayne Bridges' left foot, where Bridges' would end s + apostrophe

I hope that clarifies matters for you.

See also:
JustSomeLyrics
105
105.123
Staind Staind - Epiphany Lyrics
In too Deep Sum 41 Lyrics