EXPLANATION OF PLATE XXXI. 
Be 
Fic. 1. Partially twinned crystal of Fig. 2. Twin crystal of Joplin Calcite. 
Joplin Calcite. Twinning plane e,- % R. 
University of Chicago collection. University of Chicago collection. 
Fig. 3. Same crystal as Fig. 2, drawn in 
the position of the negative scale- 
nohedron. 
