I actually found the file folder with my sea shells in it, so will present them here for your use and enjoyment. There are plenty of tutorials and instructions on this blog, here and there, to get you started drawing and painting on canvas. The outlines, of course, could also be used for other things, both needlework and other painting related crafts.
The outlines are the shapes of actual shells, (in the range of 5 1/2" high) but I had a lot of fun painting them in exotic colors instead of the realistic ones. You could always consult a shell dictionary for that if you would rather do the "real thing."
I can see the potential here for some really pretty threads, such as the DMC Satin Floss in the "pearl" interior of the shell.
Please excuse the tilted drawing - it's late, and I was too tired (lazy) to remove the thing from the scanner and straighten it out. I hope you enjoy these, as I have several more I want to show in the next day or two.