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Prof. Lewis, On a crystal of Stephanite [May 15, 



of the planes are free from interruptions, which seem to be due to 

 narrow twin laminae, Of the planes in the prism-zone one, ?/?, 

 lying under the largely-developed p, z, n planes is smooth ; the 

 others are all striated in a vertical direction, and seem to alternate 

 frequently with one another, giving the more crowded end of the 

 crystal a somewhat rounded appearance. The dome A. (Oil) is well 

 developed on one side only, it appears on the other side in minute 

 triangles lying on the edges \ii p\ and [z p] where these edges are 

 interrupted by twin lamination. The large \ plane is very rough 

 and is covered with a number of rounded bosses rising above the 

 general level of the plane. It was impossible to obtain any 

 reflexion better than a faint illumination from this face. The 

 reflexions from most of the pyramid and dome planes were good 

 and definite. The crystal is slightly broken at the two places 

 marked in the diagram. The following table gives the ang'es 

 observed and those calculated from Miller's elements : 



