36 



NEW YORK STATE MUSEUM 



Pyramids. For the same reason that the above mentioned 

 faces are hemiorthodomes, the monoclinic forms which cut all 

 three axes are heruipyramids. Faces in the acute angle § are 

 plus hemipyramids and those in the obtuse angles are minus 



Fig. 141 Fig. 142 



hemipyramids (fig. 141, 142). As in the case of the prisms there 

 are unit, ortho, and clino hemipyramids. 



Some combinations in the group are given in fig. 143-148. 



Fig. 143 



Fig. 144 



Fig. 145 



Fig. 146 



Fig. 147 



Fig. 148 



Triclinia system 



The least symmetric of the six systems includes all forms 

 which are referable to three unequal uninterchangeable axes 



