In this case the principal axis of the body is the major axis of the second as well as of the third girdle.
A sagittal septum sometimes becomes developed, beginning with two polar beams, rising from the poles of the principal axis.
The intersection of this last line with the principal axis will give the optical center.
Four conical radial spines, two opposite on the poles of the lateral, two on the poles of the principal axis.
(C) principal axis, images formed when object is in various locations.
Cortical shell lentelliptical, its breadth (or transverse axis) surpassing considerably the length (or the principal axis).
Two opposite thin and long spines on the poles of the principal axis, numerous shorter radial spines on the whole surface.
I also desired to have a rotation of nearly 180° about the principal axis.
The principal axis of symmetry is sixfold by a combination of rotation and reflection.
This consists of a single pair of parallel faces perpendicular to the principal axis.