62 



FIRST LESSONS IN ZOOLOGT 



Having seen and examined the clam, the student should 

 compare some other common bivalves with it. Beginning 

 with the round clam, or quohog, its Indian name, the pu- 

 pil should compare every part with corresponding parts in 

 the clam. It will be seen that the shell is much thicker 

 and more solid. As the quohog is more active in its hab- 

 its, with a much larger foot (Fig. 02), it is more likely to 

 be swallowed by flounders or pollock and other fish ; hence 



Fro. 62. The round clam, or quohog (natural size), with the siphon (s) thrust out, show 

 ing the tentacles; also the scalloped edge of the mantle (M), and the large foot (/); l^ 

 Inutile; lig, ligament; A, beak. 



its shell is thicker, and thus more of a protection from its 

 enemies. 



We see that the shell is also wedge-shaped, the more 

 rounded end being the head-end, which goes into the sand 

 first. 



If we look at the shell from in front, we see the distinct 

 large beaks, and below it a heart-shaped hollow, called the 

 " lunule ; " also on the upper edge the large "ligament" 

 (Fig. 62, lig}. Opening the valves, we see that there are 



