My version:

Reference images:

Analysis (whoo, scientific): This seashell-like style starts with the hair parted the first inch or two. From there, the hair is pulled straight back into a vertical spiral against the back of the head, with blue/lavender bands in graduated sizes holding it back, starting at about the place you would put a headband and ending curled up under the hairstyle, at the nape of the neck. The hair that was parted at the beginning is swept back into the style, over the first 3 bands (see picture 1). You can see the initial part in picture 3 and how the style tapers in the back in picture 4. Picture 5 is one of the concept sketches for the style, which shows the details more clearly.

Directions: This one is quite hard to get it looking exactly how I want. First, part the first 2 inches of your hair, and put the two small pieces on either side of the part in the front out of the way. Gather the rest of your hair together at ear level in the back. If it's easier to work with, you can put it in a loose ponytail at this stage. Next, fold the hair under itself, pushing the hair up into its own pocket so that you have the bulge (for lack of a better word) at the back of your head, like in the original. Coil the folded end of the hair around into the spiral shape and pin the whole thing like mad. Now grab a long piece of ribbon or whatever it is you want to use for the bands. Thread it through the style, starting at the spot where you'd put a headband. Pin one end of the ribbon underneath the hair, and wind it around the style, moving backwards towards the nape of your neck. You'll probably have to pin the ribbon in spots to get it to stay where you want it to. After the first three bands, stop and take the pieces of hair that you left out in the front and work them into the style underneath the following bands. You can use this hair to hide any elastics, pins, or otherwise messy spots in the style. Continue wrapping the ribbon around the style until you read the end, then pin the end underneath some of the hair. That's it!