1352 
erystal-class (a :c = 1: 1,0236), possesses a very perfect cleavability 
parallel to (O01), which made it possible to prepare very beautiful, 
homogeneous plates parallel to (001), and of varied thickness; their 
accurate orientation could be controlled sufficiently in convergent 
polarized light. By means of faultless preparations of this kind, 
which had a thickness of respectively 0,34 and 1,30 mm., we 
obtained very good and agreeing ROnTGENpatterns, of which one is 
reproduced in fig. 11 on Plate IIT, and as stereographical projection 
in’ fig: 17 on, Plate IV: 
From these images it can be seen with certainty, that the crystals 
certainly possess a quaternary principal axis, but not vertical planes 
of symmetry. It follows immediately from this, that penta-erythrite 
cannot belong to this symmetry-class, but that it is tetragonal-bipy- 
ramidal, just like scheelite, or, what is far more probable in respect 
to the hemimorphy found by Martin, that it belongs in the same 
symmetry-class as wulfenite, and thus must be considered to be 
tetragonal-pyramidal. In any case the compound ean be no longer 
reckoned to be a representative of the ditetragonal-pyramidal class 
of this system. 
ITT. Tetragonal-bipyramidal Class. ; 
a. From a erystal of 7-Erythrite plates parallel to {001} and {100} 
were cut with a thickness of 0,85 and 0,81 mm., and radiated 
through. The axial ratio of this compound, whose composition is: 
C,O,H,,, is: a:¢c =1:0,3762. The obtained RönrceNpatterns were 
too feeble for reproduction; however their stereographical projections 
are reproduced in fig. 5 and 6 on Plate IV. From fig. 5 it 
appears, that the pattern of a basal section possesses only a single 
quaternary axis, but mv planes of symmetry; while from fig. 6, 
which because of the very weak negative can be only considered 
as an approximation, it may be seen, that there is only a horizontal 
plane of symmetry present. This fact also is in full agreement with 
the conclusions drawn from the theoretical interpretation of the 
representative of this phenomenon. 
6, Other results were obtained in the case of Scheelite: CaWO,, 
whose axial ratio is: a@:¢ =1:1,5359, and which according to the 
development of its limiting planes must be considered also to belong 
to this to symmetry-class. 
Originally we had at our disposition very beautiful plates, cut 
from a crystal, which evidently seemed to be a homogeneous, single 
individual; this scheelite-crystal originated from Schlaggenwald in 
Bohemia, while later erystal-plates of a crystal from Schwarzen- 
berg, Gelbe Birke, Erzgebirge were also investigated. Already soon the 
