Scheme shows double reflaction in birefringent material.
Marks used in scheme:

Thinest line shows th direction od optical axis
lines with dots and/or strokes are light rays. Dots and strokes are symbols of direction of polarization
dots - polarization perpendicular to plane of image
stokes - polarization parel to plane of image
e - ekstraordinary ray
o - ordinary ray
inerruptes line shows a wavefront
circles and elipses are some of partial waves, they are to show how Huygens` rule works here.
Own work
Sfu