Pretty sure it's Shirayukihime

:-)

I would say it is Guernsey Cream which is quite common.
I've never seen Shirayukihime offered for sale.

A bit too white for Guernsey Cream and I too have never seen Shirayukihime for sale (and I've worked for one of the largest wholesale clematis growers in the country).
It is often difficult to be certain of the ID of large flowered hybrids -- bloom time, size and even precise coloring can be heavily influenced by location and climate. If I had to put money on it, I'd guess this one to be C. languinosa 'Candida' for its quite early, very large and pure white blooms

The home I was touring on the azalea trail was fabulous...lots of rockwork, many different kinds of plants, but plants common to our area - I wouldnt think the owners would procur a hard to find clematis and feel certain it would be one easy to come by. I looked up Candida - so far, this seems the best match. The flowers were HUGE....brilliant white....light colored stamens, not coffee colored like Henryii. If this is in fact what it is.....can anyone tell me about growing this? I plan to order it - fell totally in love with it. I grow several clematis [Mrs. Cholmondeley,Violet Charm, Fireworks, Jackmanii and a couple I have lost the tags for] but after seeing this - am interested in planting more. I think I will order from Brushwood - any other vendor suggestions?
Thanks for the help!
Judith

Brushwood has an excellent reputation among members of this group. :)

It's definately Candida

^ You're right.

^ You're right.

I have ordered from Brushwood, Silver Star Vinery, and Hummingbird Farm more than once each. Quite happy with the quality of the plants and the excellent service from all 3 nurseries.

Thanks for all the help! Going to order this one right away.