of Edinbtirgh^ Session 1865 - 66 . 569 
In a few specimens, when the concentric rings round two centres 
Fig. 5 
have come into contact, as in fig. 3, the rings take the shape A BCD 
like the Lemniscates in biaxal crystals. 
Fig. 6. 
In one remarkable specimen, shown in fig. 6, the clifierent por- 
tions are disposed with such extraordinary symmetry as to give it 
the appearance of a fossil. 
