DIMENSIONS. 



163 



measured at right angles to both, and is the distance 

 from side to side, through the most bulged portion of 

 the valves. Thus a round clam has much breadth, 

 while a flattened one has but little. The thickness 

 of the shell means the thickness of the solid material 

 of each valve. 



The length of this species is from three to five 

 inches, its height is about three inches, its breadth an 

 inch and a half, and the average thickness of the 

 shell is one-eighth of an inch. The engraving repre- 

 sents the left valve, as you can see from the position 

 of the pallial simts. 



Anomia la7npe^ G-ray, A-no'mi-a lam'-pe, is a south- 

 ern species, having a very thin and delicate shell, 



which is nearly circular in 

 side in the water, and the 



much smaller than 

 Through the hole 

 byssal plug, which 

 some stone or the 



the 



shape, 

 right 



or 



It lies 

 low^er 



upon its 

 valve is 



left one, and is perforated, 

 runs a strong organ called the 

 attaches the mollusk firmly to 

 surface of another shell. The 

 upper valve is arched, and is marked internally by 



several muscle scars; color 

 yellowish, shining; length, 

 an inch or more. The Ano- 

 mia somewhat resembles a 

 small oyster, and in France 

 it forms an article of food. 

 A more northern species, 

 belonging to the same fam- 

 ily, is named Placiianomia 

 7nacroschisnia^ Desh. , Plak- 

 u-a-no'-mi-a mak-ro-shiz'- 

 ma, and a view of the same 



is 



Fig. 137- 



shown in Fi< 



137. The form of the shell 



