248 OILMAN A. DREW. 



PLATE XVIII. 



FIG. 3. 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. 4. 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. 



a, auricle ; aa, anterior aorta ; apa, anterior pallial artery ; e, excretory organ ; 

 fa, foot artery ; fv, loot vein ; ha, hepatic artery ; hv, hepatic vein ; pa, posterior 

 adductor muscle ; paa, posterior adductor artery ; pav, posterior adductor vein ; 

 ppa, posterior pallial artery; v, ventricle; i>a, visceral arteries; vm, visceral mass. 



