Shell(2 dc, ch 1, 2 dc)
(ch a multiple of 4 sts)
Row 1 shell in 4th ch from hook, *skip 3 ch, shell in next ch; rep from * to end. Turn. Row 2 Ch 3, *shell in ch-1 sp of next shell; rep from * to end. Turn.
Rep row 2.
Stitch directions reproduced with permission, from Vogue Knitting Stitchionary: Volume Four, Sixth & Spring Books, 2007