How to make the shell stitch

I am using UK abbreviations as follows:

ch = chain

dc = double crochet

st(s) = stitch (es)

tr = treble crochet

Foundation chain:

Work a multiple of 6 chain stitches plus 1 for the turning chain.

I made 6 x 32 +1=193 for my blanket which measured approx 135 cm/53" wide.

Row1: Work 1 dc into the second ch from the hook, continue to work 1 dc into each ch across. Ch 3 (counts as first tr of the next row) and turn.

Row 2: Work 2 more tr into first st (this creates a half shell), skip the next 2 sts and work 1 dc into the next st, *skip the next 2 sts and work 5 tr into the next st, skip the next 2 and work 1 dc into the next st*. Continue from * to * across the row. Ch 1 and turn.

Row 3: Work 1 dc into first st (the top of the hill), *skip the next 2 sts and work 5 tr into the next st (the dc in the valley), skip the next 2 sts and work 1 dc into the next st (the 3rd of the 5 tr on the hill), repeat from * to * across the row.

источник