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



Plate XIII. 



Fig. 1. Callistochiton crassicostatus Pilsbry. Dorsal view of head 

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

 Pedro Pleistocene) [349]. 



Fig. 2. Callistochiton crassicostatus Pilsbry. Profile of same valve; 

 same scale as preceding. 



Fig. 3. Callistochiton crassicostatus Pilsbry. Interior view of same 

 valve ; same scale as preceding. 



Fig. 4. Callistochiton crassicostatus Pilsbry. Dorsal view of less ma- 

 ture head valve from Long Wharf Canyon, Santa Monica, California 

 (Upper San Pedro Pleistocene) [509] ; same scale as preceding. 



Fig. 5. Callistochiton crassicostatus Pilsbry. Interior view of same 

 valve; same scale as preceding. 



Fig. 6. Callistochiton crassicostatus Pilsbry. Exterior view of median 

 valve from Long Wharf Canyon, Santa Monica, California (Upper San 

 Pedro Pleistocene) [512]. 



Fig. 7. Callistochiton crassicostatus Pilsbry. Interior view of same 

 valve ; same scale as preceding. 



Fig. 8. Callistochiton crassicostatus Pilsbry. Exterior view of tail valve 

 from Long Wharf Canyon, Santa Monica, California (Upper San Pedro 

 Pleistocene) [515a] ; same scale as Fig. 1. 



Fig. 9. Callistochiton crassicostatus Pilsbry. Right lateral view of 

 same valve ; same scale as preceding. 



Fig. 10. Callistochiton crassicostatus Pilsbry. Interior view of same 

 valve ; same scale as preceding. 



Fig. 11. Callistochiton crassicostatus Pilsbry. Exterior view of less 

 mature tail valve from same lot [515b] ; same scale as preceding. 



Fig. 12. Callistochiton crassicostatus Pilsbry. Profile of same valve; 

 camera outline. 



Fig. 13. Callistochiton crassicostatus Pilsbry. Interior view of same 

 valve; same scale as Fig. 11. 



Fig. 14. Callistochiton crassicostatus Pilsbry. Exterior view of juvenile 

 tail valve from same lot [515c] ; same scale as preceding. 



Fig. 15. Callistochiton crassicostatus Pilsbry. Right lateral view of 

 same valve ; same scale as preceding. 



Fig. 16. Callistochiton crassicostatus Pilsbry. Interior view of same 

 specimen; same scale as preceding. 



