500 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Plate IV. 



Fig. 1. Mopalia muscosa (Gould). Exterior view of head valve from 

 Chiton Bed, Point Fermin, California (Lower San Pedro Pleistocene) 

 |1034] ; viewed from somewhat obliquely toward the front. 



Fig. 2. Mopalia muscosa ( Gould ). Interior view of same valve; same 

 scale as preceding. 



Fig. 3. Mopalia muscosa (Gould). Profile of same valve; camera 

 outline. 



Fig. 4. Mopalia muscosa (Gould). Exterior view of median valve 

 from "coal mine", west side of Point Loma, California (Upper San Pedro 

 Pleistocene) [550]. 



Fig. 5. Mopalia muscosa (Gould). Interior view of same valve; same 

 scale as preceding. 



Fig. 6. Mopalia muscosa (Gould). Anterior elevation of same valve; 

 camera outline. 



Fig. 7. Mopalia muscosa (Gould). Exterior view of tail valve from 

 Chiton Bed, Point Fermin, California (Lower San Pedro Pleistocene) 

 [1090]. 



Fig. 8. Mopalia muscosa (Gould). Interior view of same valve; same 

 scale as preceding. 



Fig. 9. Mopalia muscosa (Gould). Profile of same valve; camera 

 outline. 



Fig. 10. Mopalia hindsii (Sowerby). Exterior view of second valve 

 from Deadman Island, San Pedro, California (Pleistocene) [578] ; same 

 scale as Fig. 4. 



Fig. 11. Mopalia hindsii (Sowerby). Interior view of same valve; 

 same scale as preceding. 



Fig. 12. Mopalia hindsii (Sowerby). Anterior elevation of same valve; 

 camera outline. 



