8 



15 show 3 -faced octahedra of various parameters with the 



derived tetrahedra. 

 9 show 4-faced cubes of various parameters. 



16 show pentagonal dodecahedra of various parameters with 



unequal combinations of the two. 

 12 show icositetrahedra of various parameters. 

 9 show the two derived triakis-tetrahedra, and their unequal 



combinations. 



29. Collection of models of the rhombohedral system, 

 with its holohedral, hemihedral, and tetartahedral forms. 



1876. Lent by Rev. Nicholas Brady, M.A. 



In this collection the faces are coloured uniformly through- 

 out. The basal planes are white. The rhombohedral or 

 pyramidal forms are coloured pink, light green, light yellow, 

 or light blue, according to their relation to the axes chosen. The 

 prismatic faces into which these rhombohedra pass respectively 

 are distinguished by darker tints of the same colours. 



30. Cardboard models of crystals of various systems. 

 2 in. size. 



1876. Lent by Rev. Nicholas Brady, M.A. 



1 6 of these represent tetrahedra, their modifications by various 

 other forms, and their twins. They are coloured light 

 and dark blue according as they are positive or negative. 



6 show rhombic pyramids and their modifications, also in 

 blue. 



2 show oblique pyramids. One pair of faces coloured white. 



5 show prismatic forms. The rectangular in red, oblique in 

 brown, and doubly oblique in pink. 



1 shows the rhombic dodecahedron in green. 



F. Orystal-Nets for making Cardboard Models. 



31. Models of crystals in cardboard (39) illustrative 

 of the crystalline systems. 



1876. Exhibited ly /. B. Jordan. 



These are coloured according to the system to which they belong. 

 The cubic forms (11) are pink, &c. The tetragonal (6) are 

 orange. The rhombic (6) are brown. The hexagonal (6) are 

 green. The oblique (5) are blue, and the anorthic (5) are 

 grey. 



(Note, the systems are called respectively by the author the 

 tesseral, tetragonal, rhombic, hexagonal, monoclinohedric, tricli- 

 nohedric.) 



