300 PROCEEDINGS OF THE AMERICAN ACADEMY. 



between (13-0- 13-1) and (1010) the missing members of normal 

 series N2, i. e. \ and 2, would develop from_ the highly improbable 

 hypothetical forms (35 -0-35 -2) and (31- 0-31-1) respectively. 



k 

 Zone 3 — Negative Rhombohedrons. Symbol ^. 



The most prominent forms of the negative rhombohedrons are un- 

 questionably (0ll2) and (0221). Assuming these poles as knots 

 we have in the portion of the zone between (0001) and 0112) : 



This portion of the zone is incomplete and contains the extra form ^5. 



j8. (0-7-7-20). This rhombohedron was recorded by Levy 27 on 

 crystal from Offenbanya, Hungary, and later by Peters 28 on a combi- 

 nation from Kapnik, Hungary. Peters did not compare the angle 

 observed on this form with the calculated angle corresponding to 

 (0 • 7 • 7 • 20) and a simple calculation will show that his measured angle 

 corresponds more closely to (0225) than to the assumed indices. 

 The form is doubtful. 



Hypothetical Rhombohedrons. Referring the above series to N2 

 the terms \ and 1 are missing. The hypothetical negative rhombo- 

 hedrons corresponding to these members of the series are (0114) and 

 (0113) respectively. 



(0114) = (552). The zones [0114- 10T0] and [0114-1120] although 

 not well marked contain several rational and well established forms. 

 The form should be retained as hypothetical. 



(0113) = (441). The zone [0113- 10T0] passes through the poles 

 of (1122), (5276), (4153), (10- 1-11 -3), etc. The form should be 

 retained as hypothetical. 



27 Levy, A., London (1837). 



28 Peters, C. F., Neues Jahrb. Min., 7861, 434. 



