DENTALIUM. 121 



hinge, or visible depression to which the connect- 

 ing muscle, as in other genera, is attached. It is 

 true, that both in this and the following genus the 

 animal does not appear to be restrained in his mo- 

 tions within the limits of his house ; but it by no 

 means follows that he has not some tie to prevent 

 his leaving it. Were he perfectly at liberty, the 

 Ibrm of his receptacle would scarcely preclude the 

 action of the water or accidental violence from 

 forcing him from it, against his will. 



