433 
1911-12.] 
The Geometry of Twin Crystals. 
p. 326; but see Miers, Min. Mag., vol. viii., 1888, p. 82), see 3 BuP] 1 Bui, 
any line in a plane of symmetry, but without other symmetry relations 
in a twin crystal where there is point twinning. 
3 Bu (in III Bu, CBu): 3 BuP, (1) principal axis of pyrargyrite in the 
twin 1BuL{ 3)\ 3BuL, (1) principal axis of proustite in twin on basal 
plane (Miers, Min. Mag., vol. viii., 1888, p. 81); (2) normal to 111 in 
3Bu, 
3>Bu,P 
twin of sphalerite on that face (Philipp Hochschild, Neu. Jahrb. Min . 
Beilage , vol. xxvi., 1908, pp. 197-205); 3 Bui, (1) normals to tetrahedron 
faces of interpenetrant twins of eulytine and diamond {III Bu class), 
(2) principal axis of pyrargyrite in line twinning with the normals to the 
planes of symmetry as twin axes (Miers, Min. Mag., vol. viii., 1888, p. 78); 
see 2 UkLI. 
vii. Lines with odd co-linear and co-directional cyclic number, at right 
angles to a line or lines of symmetry, but without point symmetry 
VOL. XXXII. 
28 
