Plate 4 



Fig. 1. Miitihis ((ilifdrnUdtus Convnd: St-a mussel. Monterey Bay. Natural size. 

 Exterior of right valve. Specimen of medium size. Note that erosion at the 

 umbonal end has destroyed the black glossy periostracum. 



Fig. 2. Mijtilus caUforuianus Conrad. Monterey Bay. One-half natural size. 

 Interior of left valve of large specimen. Note dark scar of large posterior 

 adductor muscle and smaller scar of anterior adductor in extreme umbonal end. 



Fig. 3. Modiolus rectus Conrad; Horse mussel. Elkhorn Slough, Monterey Bay. 

 Three-quarters natural size. The by.ssus is shown as well as the projecting bits 

 of epidermis that give the anterior end a bearded appearance. 



