When I saw the title of the thread I thought ” Oh, the dolphin, this should be interesting. Damn!”
Like Stoycho, I think it might be a Common Pullfball too, at it’s early stage before it gets white an fleshy.
I would recommend – http://www.amazon.co.uk/Mushrooms-River-Cottage-Handbook-No-1/dp/0747589321/ref=sr_1_1?ie=UTF8&s=books&qid=1256112614&sr=8-1
and http://www.amazon.co.uk/Mushrooms-Roger-Phillips/dp/0330442376/ref=sr_1_2?ie=UTF8&s=books&qid=1256112614&sr=8-2
as two good books for identifying fungi, particularly if you are considering collecting them for eating. The puffball can be eaten (I’ve had it myself) and can get quite big but needs to be picked while it is white and fleshy. As far as I remember, it should be never be eaten if you are drinking wine or alcohol as the combination is toxic. I might be corrected on this but I fairly sure it is the puffball. As usual with these things anyway, if in doubt, leave it alone.
David
(edit) That was probably more information than you wanted to know :)