1) Bisphenoid 
In geometry, a disphenoid (also bisphenoid) (from Greek sphenoeides, `wedgelike` ) is a tetrahedron whose four faces are congruent acute-angled triangles. It can also be described as a tetrahedron in which every two edges that are opposite each other have equal lengths. Other names are `isosceles tetrahedron and equifacial tetrahedron```. Th...
bisphenoid.