140 TERMINOLOGY. . 132. 133. 



and in the inverse position, Figs. 17 18., are (&) and 



. 132. THE TRIGONAL-DODECAHEDRON. 



The half of the digrammic tetragonal-icositetra- 

 hedron is the Trigonal-dodecahedron (. 61.) 



This resolution is likewise effected after the first me- 

 thod. 



Each of the enlarged faces is intersected by two faces 

 of the same, and one of another principal point. These 

 faces, isosceles triangles, are twelve in number ; and the 

 half therefore is a trigonal-dodecahedron. 



The crystallographic signs of these forms in the normal 



and in the inverse position, Figs. 15. 16., are (c) 



. 133. THE TETRAHEDRAL TRIGONAL-ICOSITETRA- 

 HEDRON, THE TRIGRAMMIC TETRAGONAL-ICOSI- 

 TETRAHEDRON, AND THE PENTAGONAL-ICOSITE- 

 TRAHEDRON. 



The halves of the tetracontaoctahedron are, 



1. The tetrahedral Trigonal-icositetrahedron 

 (. 70.); 



2. The trigrammic Tetragonal-icositetrahedron 

 (. 75.) ; and 



3. The Pentagonal-icositetrahedron (. 76.). 



Any one of the three methods of resolution may be ap- 

 plied to the tetracontaoctahedron; and this form conse- 

 quently has three kinds of halves, which at first sight seem 

 to agree with each other only in their being icositetrahe- 

 drons. 



