SOLEMYA, MYA 139 



adult it remains stationary. You should find a "clam bed" 

 along the shore, and after noticing the pits in the surface of 

 the mud, and the jets of water that are sometimes thrown 

 from the pits, dig down and see how the animals are placed. 

 If the water is calm, find, at the surface of the mud, the 

 openings of the siphons of specimens that are still covered 

 by water. You will need to walk very carefully so as to 

 disturb mud and water as little as possible, as the siphons 

 are otherwise closed and withdrawn. 



1. Why does this animal not need a shell that is as heavy 

 and closes as tightly as that of Venus? Does it show the 

 same points regarding the valves (umbos, beaks, lines of 

 growth, and ligament)? Later, when the shell is removed, 

 the large cartilage pit on the left valve will be seen. 



2. The ventral borders of the mantle lobes are united ex- 

 cept near the anterior end, where there is a space through 

 which the foot may be seen. 



3. The siphons are large and muscular and may be re- 

 tracted, as in the specimen that you are handling, or may 

 be greatly extended, as may sometimes be seen in aquarium 

 specimens. Why does Mya need larger siphons than Venus 



does? 



4. Pick up a specimen that has the siphons extended and 

 notice the powerful ejection of water. Is it ejected from one 

 or both openings? How is this accomplished? Of what ser- 

 vice can such jets be to the animal? Why are powerful jets 

 of this nature of more service to Mya than to Venus? 



Notice the cartilage in the cartilage pit on the left valve. 

 What function does it perform? Why is there no need for a 

 large and powerful foot? It is much easier to trace the 

 alimentary canal and the ganglion connectives in this form 

 than in Venus. 



* 



Belding: The Mollusk Fisheries of Massachusetts. Mass. Fish and 



Game Com., 1909. 

 Kellogg: Life-History of the Common Clam, Mya arenaria. Bull. U. 



S. Fish Com., 1899. 



