240 WRIGHT—CRYSTALLOGRAPHIC PROPERTIES.  [June1, 
scope lighted by auto-colimation the basal plane frequently appears 
covered with three systems of fine lines, cutting one another at an 
angle of 60° and running parallel to the outer edges of the crystal. 
The strize are usually so fine that they are invisible to the naked 
eye and have no effect on the sharp reflexion signal from the face.’ 
2. The form a, «© (1120) is rare, occurring but once on one crys- 
tal, and then somewhat rounded. From the correct position of the 
reflexion signal, however, the character of the zone and relations 
to the other faces, the form was considered probable. Its position 
on the crystal is given in Fig. 4. 
3. The form 4 (10To), «© o was observed on ten of the twelve 
measured crystals, often perfectly even and flat, at times, however, 
striated parallel to the basal edge—a phenomenon especially notice- 
able on the hollow skeleton-like crystals (Fig. 3), and due probably 
to the imperfect formation of the face. 
