Bull. U S. F. C. 1897. (Yo face page 426.) 
Plate XL 
ENCYSTED PEARLS AND PEARLS WITH MARKED INTERIORS. 
No. 1. Pearly lump from shell of Unio. 
Nos 2—5 7-9, 1 3. Encysted or ingrown pearls, Plate XI showing them from the inner side, Plate XII from the outer side, the pearls sometimes appearing 
from the exterior, through the shell (2, 3, 4), at other times not at all (7). 
No. 6. Small crayfish completely encysted. Plate XI, inner side, showing details of the animal ; Plate XII, other side, faintly. 
Nos. 10-12, 14-16, 18-21, 23-29. Pearls formed over some foreign matter differing in color from the nacre. Plate XI shows the upper or most perfectly 
coated side; Plate XII the reverse, occasionally showing the structure of the inner growth. 
No. 17. Hollow bead-like pearl, from which the nucleus has entirely disappeared — perhaps some insect or bit of vegetable matter that has decayed, or 
piece of clay that has disintegrated and washed out. It can now be blown through like a whistle. Plate XII shows the concentric layers very well. 
No. 22. Double or notched pearl, the result of the joining and intergrowth of two pearls. 
