Bull. U. S. F. C. 1897. (To face page 426.) 
Plate XXi. 
IRREGULAR AND TWISTED PEARLS. 
Figs. 1-6, showing an inner (older) pearl, mors or less covered, and enclosed by a secondary growth, the remaining figures showing peculiar twistings 
and irregular growths — Nos. 10-26, pustulate; Nos. 35, 36, elongated to a tapering point, etc. 
