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CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Plate X. 



Fig. 1. Ischnochiton acrior Carpenter. Exterior view of median valve 

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

 Pleistocene) [344]. 



Fig. 2. Ischnochiton acrior Carpenter. Interior view of same valve: 

 same scale as preceding. 



Fig. 3. Ischnochiton acrior Carpenter. Anterior elevation of same 

 valve ; camera outline. 



Fig. 4. Ischnochiton pectinuhtus (Carpenter). Exterior view of second 

 valve from Soanish Bight, San Diego, California (Upper San Pedro 

 Pleistocene) [507]. 



Fig. 5. Ischnochiton pectinulatns Carpenter. Interior view of same 

 valve ; same scale as preceding. 



Fig. 6. Ischnochiton pectinulatns Carpenter. Anterior elevation of 

 same valve ; camera outline. 



Fig. 7. Ischnochiton mertensii (Middendorff). Exterior view of me- 

 dian valve from Deadman Island, San Pedro, California (probably Pleisto- 

 cene) [709] ; same scale as Fig. 4. 



Fig. 8. Ischnochiton mertensii (Middendorff). Interior view of same 

 valve ; same scale as preceding. 



Fig. 9. Ischnochiton mertensii (Middendorff). Anterior elevation of 

 same valve ; camera outline. 



Fig. 10. Ischnochiton mertensii (Middendorff). Exterior view of tail 

 valve from Deadman Island, San Pedro, California (probably Pleisto- 

 cene) [710] ; same scale as Fig. 4. 



Fig. 11. Ischnochiton mertensii (Middendorff). Interior view of same 

 valve ; same scale as preceding. 



Fig. 12. Ischnochiton mertensii (Middendorff). Profile of same valve; 

 camera outline. 



