68 PROCEEDINGS OF THE AMERICAN ACADEMY 



In all crystals the three prisms above tabulated were present, but the 

 alternate planes of ^214} — or the planes of ^-{211}, if we regard the 

 form {2TT} composed of X-^ 2TT} and ^| 112} — were far less prominent 

 than the remaining planes of the same form. Indeed, they were fre- 

 quently diminished to such an extent that they appeared almost as lines, 

 and then no image could be obtained from them. 



Among the crystals which were studied, one only was found doubly 

 terminated. The forms were as follows : — 



One crystal was very highly modified, and exhibited all the forms, 

 with the exception of {211}. 



The following measurements were obtained : Fundamental angle 

 (between normals) (100) and (010) = 77=* 17' ; 77° Dana. 



The angle between the axes of Miller's system, 79*^ 36, or the verti- 

 cal axes of Naumann's system c =: 0.90146 ; 0.89526 Dana. 



