Colin Rowe, the maker of the diagrams, added on the mailinglist some more text to help people through the last stages. Here you find his text.

Figure 20 shows the start of the formation of the tail, and also the start of the flippers. The valley folds on the top layer of the paper are correct. In forming them, the proto-flippers stand vertically, and are then folded over as in the diagram. The head is formed by the action of the two top layers being folded down either side. This should cause the top layers on the 2D "head" to move outwards and back towards the centre, becoming 3D. Each side of the head will have a pyramid of paper pointing inwards. No new creases are made.

There is an error in figure 27, in that the paper by the head is the wrong colour; this is corrected in 28. In the formation of the flippers the first pair of swivel folds are flat, while the second set are designed to give the flipper volume, so the valley fold is flattened and the flipper is shaped to be "spoon-like".

Figure 29 - show's the result, turn over and spread the carapace.

Figure 31 - sink the two pyramids, this also takes the next layer to the side of the head.

Figure 32 - forming the head, mountain fold from the outermost part, forming a "W" of paper, extend it all the way to the end of the head, including the spread-squash underneath. This will pinch part of the carapace, (see the photo at the end) and cause the paper to swing down.

Figure 33 - the central pleat of paper folds into one of the pyramids and the upper most equilateral triangle folds into the pocket at the side. There are still no new creases. Twist anticlockwise the end of the paper on the existing creases then fold the upper-most triangle over to lock, and then push it in to the other pyramid; this completes the formation of the head. The rest is plain sailing (I hope).

Regards,
Colin.