518 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



^ (192) is considered to be one of the best established of the forms 

 here listed as new. It occurs as sharp and brilliant, though small, 

 faces and yields excellent signals. The habit and position of the 

 form are shown on crystal B7 (fig. 10) and crystal B8 (fig. 12). The 

 angles are: 



(192) Measured, minimum <p= 9 C 

 Measured, maximum <p = 10 c 

 Measured, average <p= 9 C 

 Calculated <p= 9 C 



O (1.10.2), like (192), which it always accompanies, is a well- 

 substantiated form observed as bright faces yielding sharp signals 

 on several crystals. The angles are: 



(1.10.2) Measured, maximum <p = 9° 10' p = 81° 06' 



Measured, minimum <p = 9° 08' p = 81° 04' 



Measured, average ^ = 9° 09' p = 81° 05' 



Calculated ^ = 9° 08' p = 81°01' 



A = 0° 01' A- 0° 04' 



The two forms (192) and (1.10.2) occur together, and the differ- 

 ences in their angles are so small that the signals overlap slightly. 



dl (1.12.2) occurred as two fairly large, though etched, faces on 

 crystal 14. The angles are: 



(1.12.2) Measured <p = 7° 35' p = 83° 18' (average of 2). 

 Calculated <p = 7° 30' p = 82° 34' 

 A = 0° 05' A= 0°44' 



@ (331), new, is one of the few positive pyramids occurring in the 

 zone (001):(110). It occurs as a narrow line face, with t (11.11.10) 

 between (110) and (111), on crystal B6, and as a similar narrow, 

 though distinct, face yielding a poor signal on crystal 55. The 

 angles are: 



(331) Measured <? = 57° 34' P = S1° 58' Crystal B6. 

 Calculated ^ = 57° 37' 



A= 0° 17' 

 Measured ^ = 57° 29' p = 80°37' Crystal 55. 



A= 0° 08' 



X (343) was found as a very narrow but bright face, beveling the 

 angle between j3 (121) and n (111) on crystal 51, as shown in figure 17. 

 Here it occurs with the other forms of the same vertical zone — 

 namely, (344) and (345). The angles are: 



(343) Measured ^ = 48° 30' p = 69° 13' 



Calculated ^ = 49° 49' p = 69° 04' 



A= 1° 19' A= 0° 09' 



