PLATE 18 
All figures approximately natural size 
Fig. 1. Modiolus demissus (Dillwyn). Longitude 77.2 mm. San 
Francisco Bay. Exterior of left valve. 
Fig. 2. Mytilus californianus Conrad. Longitude 77 mm. Pre- 
sidio. Exterior of left valve. 
9 
Fig. 3. Lyonsia californica Conrad. Longitude 22.4 mm. San 
Francisco, University of California Collection. Exterior of right 
valve. 
Fig. 4. Mytilus edulis Linnaeus. Longitude 51.3 mm. Station 
D 5764. Exterior of left valve. 
Fig. 5. <Adula stylina Carpenter. Longitude 33.7. Moss Beach, 
San Mateo County, Collected by A. L. Barrows. Exterior of left 
valve. 
Fig. 6. Adula falcata (Gould). Longitude 70 mm. Duxbury 
Reef, Bolinas. Exterior of left valve. 
[368] 
