I thought those clams looked like Maxima in the picture. I also wanted to find out more about the hippo clams because they are not available in the trade very often.
I found this site
http://animal-world.com/encyclo/reef/clams/tridacna.htm
apparently these hippo clams arent even of the tridacna family....
This is a picture of a hippo clam...
and more info on the hippo clam..
http://animal-world.com/encyclo/reef...ppopusClam.php A little less blue then the maxima picture but rare and nice in a different sort of way.