ENSIS DIRECTUS. 129 



Belding; The MoUusk Fisheries of Massachusetts. Mass. Fish and Game 



Com., 1909. 

 Kellogg: Life-History of the Common Clam, Myra arenaria. Bui. U. S. 



Fish Com., 1899. 

 Mead and Barnes: Observations on the Soft-shell Clam. Rhode Island 



Com. Inland Fish., 20 to 24, 1900 to 1904. 

 Yonge; Studies on the Comparative Physiology of Digestion. I. The 



Mechanism of Feeding, Digestion, and Assimilation of the Lamelli- 



branch Mya. Brit. Jour. Exp. Biol., 1, 1923. 



ENSIS DIRECTUS. (Razof-sheU Clam.) 



This species is another representative of the order Eulamel- 

 libranchia and is introduced because of its adaptation for a 

 burrowing habit, and because of the great ease with which its 

 nervous system can be studied. Individuals are not uncommon 

 on mud- or sand-flats from which the water flows at low tide. 

 They may sometimes be seen protruding above the surface of 

 the mud, but are hard to approach because of their great sen- 

 sitiveness. Upon being disturbed they quickly disappear be- 

 neath the surface of the mud. These animals are sometimes 

 used for food. They are frequently collected in Japan by plac- 

 ing a little common salt in the opening of the burrows. Within 

 a few seconds an animal so treated energetically backs out of its 

 burrow. 



1. Notice the shape of the shell, the way it gapes at both 

 ends, and the way the lobes of the mantle are fused. 



2. With a pencil-point or seeker stroke the tentacles around 

 the siphon openings, while the animal is being held anterior end 

 downward. This will cause it to perform the burrowing move- 

 ments. Study the movements carefully and see w^hat the effects 

 would be were they performed in mud. Thrust the anterior end 

 of the shell in mud and watch .the result of the movements. 



3. Water is ejected by the sides of the foot to aid in burrow- 

 ing or to enable the animal to swim, but observations on its 

 method of ejecting it are not easily made, and are sure to take 

 much time. Notice the way the anterior margins of the lobes 

 of the mantle scrape mud from the foot when the foot is being 

 -withdrawn. 



4. Vvith a scalpel separate the united margins of the mantle 

 9 



