CHAPTER VI 



UNIVALVE MOLLUSKS 



A few years ago I visited the pretty little town of 

 Bolinas, situated, on the iirst bay to the north of the 

 Golden Gate. From the shore there runs out a ledge 

 of rock far into the ocean, which is commonly known 

 as Duxbury Reet. One morning when the tide was 

 low I went far out on this reei and found that it 

 furnishes an excellent home for many living crea- 

 tures. Turning back the masses of olive-green sea- 

 weed I found a considerable number of mollusks 

 with shells like the one shown in Figure 91. It is not 

 a very common species for California, but is more 

 abundant in the north. 



The shell of a full grown specimen is an inch and 

 a half long. It is spindle-shaped, that is, it is largest 

 in the middle and tapers towards each end. Various 

 parts of the shell have received names, and as this 

 is the first species which we are to consider which 

 belongs to the great class of the Gasteropods we will 

 now notice these names. The Gasteropod shell is 

 really a long tube, coiled in a spiral form. This 

 fact may not seem so evident in this species as in 

 certain others, but it is the plan of the shell neverthe- 

 less, and a knowledge of this fact will help to an- 

 swer many troublesome questions. 



The opening to this tube is called the aperture, 

 and it is named ap in the figure. As you face the 



