Fig. 38. 



Fig 39. 



Figs. 38 and 39. Photographs of pearl oysters (Margaratifera var. mazallantica) showing newly 

 formed pearls which have developed on various parts of the mantle. 



In each specimen the thin sac has been cut open to expose the pearl sufficiently for good photo- 

 graphic results. The pearls are shown in about natural size, but the oysters have been shrunken 

 in spirits. All of the pearls are located on some portion of the free mantle, generally on the branchial 

 surface, some being on the inner surface. The pearls are apparently spherical and vary in size from 

 about one to three grains. 



Specimens presented to the American Museum of Natural History by Gaston J. Vives of La Paz. 



443 



