An isosceles triangle is a triangle with two of its three sides equal. A RIGHT ISOSCELES TRIANGLE has its two SIDES meet at 90 DEGREES. If you put two RIGHT ISOSCELES TRIANGLES tog ether, long side to long side - you get a SQUARE CUBE. The DIAGONALS of a SQUARE CUBE
Isocones are the next simplest Streptohedron. Imagine a CUBE of wood mounted on diagonal corners and turned to Back To Back Cones. Now if the cube is actually made up of TWO pieces of wood - with a clued paper joint in the right place, you can part the back to back cones And if you turn the bottom half 90 degrees and glue the pieces back together - you have an Isocone.
Maybe these illustatrations will make things clearer. By clicking on the image, you can download the SketchUp file of these virtual 3D objects and, with SketchUp or SketchUp Viewer, get to know and understand how this Streptohedron idea works.