Hi Sandy,
Think of the block as 4 mini log cabin blocks. two are the same and two have the colors opposite. When you have all four mini log cabin blocks, then sew them together like a four patch.

I see the clamshell in this curved log cabin graphic I drew for the workshop sample I'm teaching in April. The finished quilt will be similar but not exact to this one.

These curved blocks are easy to make; I wish we could see a picture of the one that interests you so we could help more.

Jan in VA

Hi Jan in VA,
Check back on response #5 from Woody. The second link provided shows the block diagram.

---Ps---- great quilt layout you have shown us!

Thanks Jan, I can see your clam shell...I tried to post a picture, no luck, but this is the website if you have time to look at it. Appreciate your help
http://judyholleyquilts.com/mywebedi...sSupplyist.pdf

Jan, I wish I were closer. That is gorgeous.

Dear QM, Thanks so much, I blew up the block and now I see what you are talking about....It takes me a while, and i have been going back and forth to this site to reread and it all comes clear now. Thanks again, Sandy