Homohedral module genus extender

A toy block of convex-concave design in which the convex surface is identical to a surface on two joined, double truncated icosahedra, the truncations being formed by removal of a cluster of five icosahedral faces which form a pentangular pyramid about a vertex, said truncated icosahedra being joined along two truncation surfaces thus formed;

• and in which the concave surfaces are located at the remaining two truncation surfaces and are of such a degree of concavity that when a wholly convex surface surrounding a vertex on a similar block, an analogous icosahedron block or homohedral module, is fitted within it, a set of pentangular edges on each block are made tangent to one another.