FIG. 8. Ventral view of the foot showing the split end and the open- 

 ing of the byssal gland. Magnified three diameters. 



PLATE 5- 



FIG. 9. Outer surface of the left lobe of the mantle showing the arrange- 

 ment of blood vessels. Two-thirds natural size. 



FIG. 10. Animal as seen from the left side with the left shell valve and 

 mantle lobe removed. The rounded bodies at the bases of 

 the marginal row of tentacles are the eyes. Two-thirds nat- 

 ural size. 



PLATE 6. 



FIG. ii. Animal as seen from the left side with the left shell valve and 

 mantle lobe removed and with a portion of the pericardial 

 wall cut away. A few of the blood vessels are shown. Two- 

 thirds natural size. 



FIG. 12. Animal as seen from the left side with the left shell valve and 

 mantle lobe removed, with the alimentary canal shown. Two- 

 thirds natural size. 



PLATE 7- 

 FIG. 13. Animal as seen from the left side with the left shell valve and 



mantle lobe removed. Drawn to show the arterial system of 



blood vessels. Two-thirds natural size. 

 FIG. 14. Animal as seen from the left side with the left shell valve and 



mantle lobe removed. Drawn to show the systemic veins. 



Two-thirds natural size. 



PLATE 8. 

 F|G. 15. Animal as seen from the left side with the left shell valve and 



mantle lobe removed. Drawn to show the nervous system. 



Two-thirds natural size. 

 FIG. 16. Inner surface of the right lobe of the mantle showing the 



arrangement of the pallial muscles. Two-thirds natural size. 



PLATE 9. 



FIG. 17. A portion of a gill showing the arrangement of parts. The 

 figure indicates the inter-lamellar junctions cut at different 

 levels. The further lamella is the one that was attached to 

 the suspensory membrane and the vessel (ba') was directly 

 connected with the vessel that supplied the gill with blood 

 (ba, Fig. ii ). This vessel follows along the edge of the 

 inter-lamellar junction to the free edge of the unattached 

 lamella, (the one on the side nearest the observer in the 

 figure) where it bends back and passes down the modified 



