1) To fully understand what they were like shells realize some models of Pongo. We take a piece as big as a walnut and roll around on the bench to form an elongated cone.
2) Then we start to roll the tip with our left hand turning counterclockwise.
3) At the end there is no difficulty in recognizing the realized: a shell! By changing the screwing up or on the floor, or by squeezing the sides of the cone to form a pyramid with a square or triangular base, we will obtain shells of different shapes.
4) Here is the result.