Citrus Joe sent me some seed of the Diamante citron four years ago that he got from a visit to UCR. This year is the first it is producing flower buds, not bad for 4 years from seed. I'll post some photos later. It got attacked by mites this winter but is now flushing and doing great.

http://www.citrusvariety.ucr.edu/citrus/diamante.html

The Diamante citron is commercially grown in Italy - mainly in the Calabria region but also in Sicily. The variety is instantly recognisable by its square 'shoulders' and tapered end. It often has slight corrugations.
The Riverside pictures show a fairly typical citron, but not quite the very distinctive shape of the Italian Diamante.
There is a picture of an Italian Diamante citron on my website at
http://www.homecitrusgrowers.co.uk/citrusplaces/tintori/tintori2007.html
Also at
http://www.flickr.com/photos/terzocchio/3249234766/
Mike aka Citrange

Citrus Joe, also gave me some Diamante citron seeds about the same time as Lass's. He did get them when he and I went to CCPP. However, I never planted mine, as Diamante are not good to eat. Now I wish I had, but now that's water over the damn. - Millet (1,368-)