CATECHISH OF CONCHOLOGY. 23 



primary teeth are still to be attended to; for 

 they constitute the best, though not always the 

 most obvious criterion. 



Q. Is there nothing else ? 



A. Observe that the bend or fold of the extre- 

 mity of the compressed slope is, without any 

 exception, towards the left valve ; that is, towards 

 the right hand of the observer, when the shell is 

 placed upon its base, with the area in front. 



Q. Where are the Tellinae generally found ? 



A. In fine sand or gravel on the sea-shore, 

 some of them in rivers and wet ditches. 



