EXPLANATION OF PLATE 12 



Fig. la. Mactra stultora Linnaeus, x 1. 



Interior of the left valve of the typical species of the genus 

 Mactra. Foreign, Recent. 



Fig. lb. Mactra stultora Linnaeus, x 1. Foreign, Recent. 



Fig. 2a. Mactra nasuta Gould, x 1. Recent. 



Fig. 2b. Mactra nasuta Gould, x 1. Recent. 



Fig. 2c. Mactra nasuta Gould, x 1. Recent. 



Fig. 3a. Mactra dolabriformis (Conrad), x 2. Recent. 



Fig. 3b. Mactra dolabriformis (Gould), x 2. Recent. 



Fig. 3c. Mactra dolabriformis (Conrad), x 2. Recent. 



Fig. 4a. Mactra exoleta Gray, x 1. Pleistocene. 



Fig. lb. Mactra exoleta Gray, x 1. Pleistocene. 



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