Topping up oil on Peugeot 306 diesel? Cont...?

Can anyone who answered my previous question please have a look at this link? This is the only photo I could find of under the bonnet on a 306. Mine is a diesel but the caps and pretty much everything else is the same. Right at the bottom there is a cap with a triangle and a book-looking picture on it. On my car this cap is purple but on here it's black but has the same pictures on it. Its just down and to the right of the blue cap which is on the left, which is the screen wash. Thanks everyone. The link is... http://us1.webpublications.com.au/static/images/articles/i4/0403_6mg.jpg