Plate 3 



Fig. 1. Monia macroschisiua Deshayes ; Rock oyster. Monterey Bay. Natural 

 size. Exterior of upper (left) valve. 



Fig. 2. Monia macroschisvia. same specimen as Fig. 1. Exterior of lower 

 ( rislit ) valve. Note the deep notch (apparently a hole) for the passage of a 

 tayssus. 



Fig. 3. AnoDtia peruviana Orbigny ; Rock oyster. San Diego. Two and one- 

 lialf times natural size. Exterior of upper (left) valve. 



Fig. 4. Mjitilns ednlis Linnaeus ; Bay mussel. Huml)oldt Ba.v. Twice natural 

 size. Tlie b.vssus with adliering liits of stone, etc., is clearly shown. 



