244 Penfield and Ford*— Developments of Calcite Crystals. 



tion because of the peculiar combination of forms. Besides 

 the basal planes only two forms are present, the negative 

 rhombohedrony, 0221, a very common form, and the positive 

 scalenohedron F, 4261, a rare form for the species. The 

 scalenohedron J^has the same parameter relation on the hori- 

 zontal axis as the common scalenohedron v, 2131, but is twice 

 as steep, F intersecting the vertical axis at 6 and v at 3. Fig. 

 16 was drawn by Dr. H. E. Gregory while a student in the 

 laboratory. 



Sheffield Laboratory of Mineralogy and Petrography, 

 Tale University, New Haven, May, 1900. 



