__Spheno-mega-coronas__

Type (A): **n/d-4-3-3-4, **Type
(B): **4-3-3-3-3, **Type (C): **3-3-3-3, **Type (D): **3-3-3-3-3,
**Type
(E): **n/d-3-3-3-3-3**

The only **n**-gonal convex member
of this family is the Johnson Solid sphenomegacorona
or the "Digonal Spheno-mega-corona" with **n=2**. If **n=3** then
the resulting Triangular Spheno-mega-corona
is clearly not convex.

Examination shows this family to be
locally convex in the range **2 <= n/d < ~2.8**. The local convexity
is evident on this 7/3 spheno-mega-corona with only
one rotation around the symmetry axis. The following models with
only one rotation around the symmetry axis show that **n/d=2.666** (8/3)
is clearly convex, **n/d=2.75** (11/4)
appears to be marginally convex whilst **n/d=2.8** (14/5)
appears to contain coplanar faces. (Full 14/5).
It must be stressed that the upper convexity limit has to date only been
assessed from a visual examination of the VRML models and has not been
explicitly determined.

Spheno-mega-coronas with **d>1**
and **n<=12** for **2<n/d<3** are listed below. As with
the spheno-prisms, the solids have a number of internal vertices.
The type (B) vertices are not normally visible from the outside of the
solid.

5/2 | 7/3 | 8/3 | 9/4 | 11/4 | 11/5 | 12/5 |

Retrograde spheno-mega-coronas are also possible: for example this 7/4 spheno-mega-corona

Like the spheno-coronas, there are additional isomorphs to the spheno-mega-coronas, for example the above image is of a 7/3 spheno-mega-corona isomorph. These have not been classified, but a further 7/3 spheno-mega-corona isomorph is linked here:

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