I sewed three clams together. Place two clams, on top of each other, right sides together. Sew about 1/2 inch up from the bottom up, press the seam open. Sew a clam into that curve just made. Here are the three sewed together and then I just layed another one to the top line and layed one in that curve.
So, I would sew a whole row of clams across and insert the bottom ones. The can be done in 3's and then the 3's joined and a clam inserted into that curve. Well, that is what I've come up with so far.