522 CALIFORNIA ACADEMY OF SCIENCES [Pkoc. 4th Ser. 



Plate XV. 



Figs. 1-6. Callistochiton palmulatus mirabilis Pilsbry. Dorsal aspect of 

 six tail valves from Long Wharf Canyon, Santa Monica, California (Upper 

 San Pedro Pleistocene) [528], showing variation at corresponding stages 

 of growth. 



Figs. 7-12. Callistochiton palmulatus mirabilis Pilsbry. Right lateral 

 view of same six valves; same scale as preceding. 



Fig. 13. Callistochiton palmulatus mirabilis Pilsbry. Interior view of 

 valve shown in Figs. 1 and 7 ; same scale as preceding. 



Fig. 14. Callistochiton palmulatus mirabilis Pilsbry. Interior view of 

 valve shown in Figs. 4 and 10; same scale as preceding. 



