PLATE XVIII 



Abalone Shells and Pearls. 1. Black Abalone (H allot is 

 cracherodii). 2. Red Abalone (H. rufescens). 3. Green 

 Abalone (H. fulgens). 4. The Common Boring Mollusc 

 (Pholadidea parva) Which Causes the Formation of 

 Blister Pearls. 5. Another Mollusc (Adula stylina) 

 Which Bores Into the Heavy Rim of the Abalone Shell. 

 6. Exterior of the Abalone Shell Showing the Aperture 

 of the Bore of the Parasitic Mollusc. 7. An Abalone 

 Pearl. 

 Phot(«raph by T. I. Storer. 



