646 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



and c only moderately well placed would hardly establish this form if 

 it were not already known. 



u (34-4). One face each on three crystals, all of poor quality and 

 only one really definite, are all that could be referred to this form. 

 These fell near the computed position. 



*d (455). This form is new. All four faces of good quality occur 

 on one crystal of prismatic habit in close agreement with the computed 

 position. The form must be regarded as established. The data 

 follow : 



<b o 



image of good quality 



whence, 



40 52 38 28- is the mean observed position of this form. 



40 29 38 27 is the calculated position of this form. 



Another crystal of prismatic habit shows one face in approximate 

 agreement with this position, but it is less definite. Because it is so 

 poorly placed that it might equally well be referred to the pyramid *g, 

 another new form described below, it is not included in the tables nor 

 allowed to disturb the mean of the observed values for either d or g. 



*g (788). All four faces of this form are found on the same crystal 

 of prismatic habit that showed the form d, the best developed crystal 

 of the suite. It does not agree as well as could be desired with its 

 computed place, but it occurs more definitely on this crystal than some 

 of the established forms occur on any of the crystals examined ; there- 

 fore it is accepted and presented, but it needs confirmation. The data 

 follow : 



whence, 



42 08 39 05- is the mean observed position for this form. 



43 02 39 34 is the calculated position of this form. 



A face is described under d which might better be referred to this 

 form, except that this is in greater doubt. 



Uncertain forms : Except the first two listed, these forms all fall in 

 the same zone with the two last described, between p and e- They are 



