This can be known by other names; diamond darts, double pointed darts or contour darts. But as the latter suggests, they are for contouring over the curves of the figure throughout the main body of a garment.
The points and the width of the dart are marked. As with all darts, sewing should start at the widest part so these darts are sewn in two halves.
How to sew a Fishtail Dart
1. Mark out the dart on to the wrong side of the fabric.
2. Starting at the widest part of the dart, sew a small flat section in the centre of the dart line and then up towards the point.
3. Curve off your sewing as you reach the point. Secure your stitching.
4. Go back to the beginning and overlap your first line of stitches. Sew up towards the other point of the dart.
You should have a row of sewing that starts at the top of the hill dips down into a valley and comes back up to the crest of another hill. Smooth lines of sewing that echo the curves of the body.