Rhombic-bipyramidal Class, 2/m 2/m 2/m
The geometric solid taken (according to the above established criteria) to represent the stereometric basic form (promorph) of all the crystals of this Class is the Rhombic Bipyramid, or Rhombic Octahedron (Figure 1).
This body is an amphitect bipyramid with four (or two) antimers.
The promorph is accordingly that of the Allostaura octopleura (Stauraxonia homopola).

Figure 1.   A Rhombic Bipyramid or Rhombic Octahedron, the Stereometric Basic Form of the crystals of the Rhombic-bipyramidal Class of the Orthorhombic Crystal System.
The equatorial plane is a rhombus.
( After HURLBUT, C. & KLEIN, C., 1977, Manual of Mineralogy )

Figure 2.   A Rhombic Bipyramid or Rhombic Octahedron, the Stereometric Basic Form of the crystals of the Rhombic-bipyramidal Class of the Orthorhombic Crystal System.
The equatorial plane (yellow) is a rhombus. The three crystallographic axes are given in red. The one that is vertically drawn is the choosen promorphological main axis, the other two are the radial cross axes.

Figure 3.   A Rhombic Pyramid, the Stereometric Basic Form of the crystals of the Rhombic-pyramidal Class of the Orthorhombic Crystal System.
The base is a rhombus. The three crystallographic axes are given as reddish solid lines. The one that goes to the pyramid's tip is the promorphological main axis, the other two reddish solid lines are the two promorphological radial cross axes, while the dashed lines are the two interradial cross axes.

Figure 4.   A Rhombic Bisphenoid, the Stereometric Basic Form of the crystals of the Rhombic-bisphenoidic Class of the Orthorhombic Crystal System.

Figure 5.   A Rhombic Bisphenoid, the Stereometric Basic Form of the crystals of the Rhombic-bisphenoidic Class of the Orthorhombic Crystal System.
The promorphological main axis is indicated by a red line.

Prismatic Class, 2/m
The geometric solid taken (according to the above established criteria) to represent the stereometric basic form (promorph) of all the crystals of this Class is the Amphitect Gyroid Bipyramid (with two or four antimers) (Figure 6).
This body can be seen as two gyroid pyramids connected to each other by their bases. The equatorial plane is planar, and the composing pyramids are not rotated with respect to each other.
The promorph can be assessed as that of the Allosigmostaura quadramphimera (Stauraxonia homopola sigmostaura) (When there are just two antimers present then :   duamphimera).

Figure 6.   Slightly oblique top view of an Amphitect Gyroid Bipyramid, the Stereometric Basic Form of the crystals of the Prismatic Class of the Monoclinic Crystal System. The depicted bipyramid allows for four antimers to be recognized. The lower pyramid is not visible, but nevertheless present.

Figure 7.   Slightly oblique top view of an Amphitect Gyroid Pyramid, the Stereometric Basic Form of the crystals of the Sphenoidic Class of the Monoclinic Crystal System. The depicted pyramid allows for four antimers to be recognized.

Figure 8.   Slightly oblique top view of half a Rhombic Pyramid, the Stereometric Basic Form of the crystals of the Domatic Class of the Monoclinic Crystal System. The depicted pyramid has two antimers, indicated by coloration.

Figure 9.  
The basic form of the Heterostaura allopola, illustrated by half a Rhombic Pyramid (which itself is the basic form of the Allopola zygopleura eudipleura) .
Left image :   bisection face (originated by the bisection of the whole Rhombic Pyramid) emphasized (green).
Right image :   Base emphasized (green).
Main axis (vertical), lateral axis (horizontal) and dorso-ventral axis are indicated in red. The only symmetry element is the mirror plane, which contains the main axis and the dorsoventral axis. It separates the two antimers.

Pinacoidal Class, 1*
Something possessing a symmetry " 1* " means that the only symmetry element that is present is a center of symmetry. Such a center is a point in the structure such that equal features are found at equal but opposite distances from that point. (The asterix (*) we do not find in the crystallographic literature :   there it is replaced by a horizontal score above the relevant numeral). The geometric solid taken (according to the above established criteria) to represent the stereometric basic form (promorph) of all the crystals of this Class is a Triclinic Bipyramid or Oblique Rhombic Bipyramid. (Figure 10 and 11). Such a bipyramid has no symmetry axes, but it does have a body center, namely its center of symmetry. Of course it has a 1-fold rotation axis, but such an axis is never unique. Every geometric solid is mapped onto itself by any such axis whatsoever, because every geometric body maps onto itself by a rotation of 360⁰ about any axis (such an axis is a 1-fold rotation axis). In the pyramid we can nevertheless draw three axes. They are the crystallographic axes, i.e. the three triclinic axes. They intersect in the center of symmetry, but do not involve angles of 90⁰. The (crystallographic) axial system is wholly oblique. Promorphologically the poles of these axes do not represent specific body parts, i.e. specific anatomical parts of the organic individual that realizes this basic form. We can draw as many axes through the center of symmetry as we wish to. None of these axes stands out (neither does a subset of those axes), and this is equivalent to there being no genuine axes at all. The situation looks a little like we see in the Homaxonia -- spheres -- but here all axes are identical.
The promorph is accordingly that of the Anaxonia centrostigma, i.e. bodies having no (promorphological) axes but which do have a body center.

Figure 10.   Triclinic Bipyramid, Stereometric Basic Form of the Pinacoidal Class of the Triclinic Crystal System.
The angle between the equatorial plane and the main axis is different from 90⁰.

Figure 11.   Triclinic Bipyramid, Stereometric Basic Form of the Pinacoidal Class of the Triclinic Crystal System.
The angle between the equatorial plane and the main axis is different from 90⁰. Triclinic axial system inserted. The three axes do not involve angles of 90⁰.

Figure 12.   Equatorial plane of a Triclinic Bipyramid, as seen from a direction perpendicular to that plane (and thus not seen along the direction of the bipyramid's main axis).
The angle between the equatorial plane and the main axis is different from 90⁰. Two triclinic axes inserted (red), they meet in the bipyramid's center of symmetry ( i ).

Figure 13.   Parallelopipedum, having the symmetry of the Pinacoidal Class of the Triclinic Crystal System. All angles are different from 90⁰. There are no symmetry axes, nor mirror planes.

Figure 14.   Parallelopipedum, having the symmetry of the Pinacoidal Class of the Triclinic Crystal System. All angles are different from 90⁰. There are no symmetry axes, nor mirror planes. When we nevertheless try out a 2-fold rotation axis, we see that such an axis will map the face (of the parallelopipedum) on which it is perpendicular, indeed onto itself. But such an axis will not map the whole parallelopipedum onto itself, because that axis is not perpendicular to the opposite face (it is not parallel to AB). This opposite face will not be mapped onto itself by an oblique 2-fold rotation axis.

Figure 15.   Half a Triclinic Bipyramid, the Stereometric Basic Form of the crystals of the Asymmetric Class of the Triclinic Crystal System. The depicted geometrical solid is (in fact) a single pyramid :   a totally irregular pyramid.

Figure 16.   Equatorial plane of Half a Triclinic Bipyramid.