many people mix up the "shell" and "swirl" patterns. both have the lovely swirl pattern on the sides. here are ways to identify which is which.
shell was made by Anchor Hocking and is stamped with their mark on the bottom. this pattern was made in the jadite and anchorwhite (milk glass) colors. the anchorwhite design has a 22k gold edge on it. the way to identify this pattern is by the scalloped edge around the plates, bowls, platters and saucers. the teacups also have a distinct shape: skinny at the bottom and fuller at the top.
swirl was made by Anchor Hocking's brand, Fire King. You will see the Fire King stamp on the bottom of the pieces. this design came in quite a few colors: jadite, azurite, pink, ivory & white. they made mixing bowls, teacups, plates, platters, serving bowls & dessert bowls in this design. the edges do not have the scalloped edge, so they are easy to identify.