230 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.53. 



Plate 30. 

 (Enlarged 20 times.) 



Fig. 1. Shows at top a simple crystal with central inclusion, outer clear zone, 

 and thin line of dark matter near margin, the heaping up of a dark rim at 

 sides, and the slight parting of the cells at either end. Near the bottom a 

 twinned crystal, with the inclusion continuous with the outer cells at one end 

 and partitioned among the twinning lamellae at the other; the lack of distortion 

 of the cells is evident. 



Fig. 2. Shows near center large irregularly twinned crystals, with the in- 

 cluded cells partially continuous with those outside, but greater distortion 

 toward the margin than in the center of the crystal. 



Plate 31. 

 (Enlarged 20 times.) 



Fig. 1 (part of Plate 29, further enlarged). Shows compound twin crystals 

 with marked partition of inclusions among the several parts of the twins, 

 yielding insectlike forms. The dark rims of excluded cell material are also 

 well developed. 



Fig. 2. Shows symmetrical partition of inclusion in a "fish tail" twin 

 crystal. 



Fig. 3. Shows at top a crystal seen end on, the central Inclusion being slightly 

 eccentric. Below, a multiple twin with unusually faint inclusions. 



