310 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Form \ Q: a ' 



13 



2 

 7 

 2 



Symbol 6 

 v-S 3 

 N 3 3 (J) 



This fragment of the zone is somewhat incomplete with respect to 

 N3 and contains a great many extra forms some of which fall in normal 

 series N 4 . 



1) : (11 -5-16-21) = (16-5-0). This scalenohedron was observed 

 by Schaller 50 on crystals from Terlingua, Texas. The form was 

 determined from extremely small planes, giving weak signals. The 

 vertical zone [0001 : 11 -5- 16-21] also contains the form (11-5-16-6) 

 which marks several zone intersections. The form which falls in 

 normal series N5 seems fairly probable. 



: (9-2-11-13) == (11-2-0). This scalenohedron was noted by 

 Melczer 51 on crystals from Budapest. The pole (9 -2- IT -13) does 

 not fall in any zone other than the one under discussion and although 

 the term § is referable to normal series N4 the form should be regarded 

 as somewhat doubtful. 



a: (11-2- 13- 15) = (13-2-0). This scalenohedron was noted by 

 Sansoni 52 on three crystals from Andreasberg. The measured angles 

 as determined by him agree well with theory although the pole lies 

 very close to (6178), a form which agrees better in zonal relations. 

 The scalenohedron (11-2-13-15), however, is referable to normal 

 series N 5 and should be regarded as somewhat probable. 



c: (6178) = (710). This scalenohedron was first noted by Haus- 

 mann 53 on crystals from Andreasberg. The form was later observed 

 by Hessenberg 54 and is regarded by Irby as well established. The 

 zone [6178 : OHO] is, moreover very well marked and the form falls 

 in normal series N4. It should be regarded as well established. 



b: (7189) = (810). This scalenohedron was first recorded by 

 Sella 55 on crystals from Sardinia. It was subsequently noted by 

 Hessenberg from Andreasberg and by vom Rath from Lake Su- 

 perior. It falls in normal series N5 and although not as rational 



50 Schaller, loc. cit. 



5 1 IvI f I (~* 7 f*T* I O (* o 1 \ 



•52 Sansoni,' F., Acad. d. Line, 19, PI. 3, Fig. 20 (1884). 



53 Hausmann, J. F. L., Handbuch der Mineralogie (1847). 



54 Hessenberg, loc. cit. 



55 Sella, Q., Mem. Ae. Turin., 2, 17, (1856). 



