306 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



U. (0-36-36-1). This rhombohedron was noted by Johansson 46 

 on crystals from Norberg, Sweden. In this instance, since the form 

 was observed on crystals of rhombohedral habit, it was impossible 

 to verify the identification of this rhombohedron from zonal relations 

 with scalenohedral forms. The hypothetical rhombohedron (0-35- 

 35-1) differs from (0-36 -36-1) in but 2|' of p value, has much simpler 

 Miller indices [(0- 35-35-1) = (12-12-23), (0-36-36-1) = (37-37- 

 71)] and falls in normal series N4. The rhombohedron (0-36 -36-1) 

 should be regarded as doubtful. 



Hypothetical Rhombohedrons. — None of the forms missing from 

 normal series N3 as developed above suggest by zonal relations the 

 possibility of hypothetical rhombohedrons between the limits dis- 

 cussed. The two hypothetical forms (0-29-29-1) and (0-35-35-1) 

 suggested in the above discussion should not be retained as such. 



46 Johansson, K., Geol. Foren. Forh. 14, 49 (1892). 



