182 THE RING OF NATURE 



tunity of seeing how nimbly the animal can jump 

 in the soft muddy sand in which it lives. 



The shell of the cockle tells its life-history to 

 any boy scout. The thicker it is the rougher the 

 sea from which it came, wherefore Cornish cockle- 

 shells will be found to be much thicker and stronger 

 than Dawlish cockle-shells. The inner surface of 

 the shell has tell-tale marks upon it pits where 

 the two strong muscles were attached that open 

 and shut the shell, and a thin line all along to show 

 where the mantle joined the shell. This line runs 

 into a deep bay at one end, and that is where the 

 siphon poked out. If we find no bay in the 

 mantle-mark, we know that the bivalve whose 

 remains we are examining had no siphon. 



Away with the univalve gasteropods and the 

 bivalves. We may find a shell like a tiny 

 elephant's tusk, open at both ends. It belongs to 

 another order of the everlasting molluscs, the 

 scaphopods. The little lamp shell with the lower 

 shell very concave like the old-fashioned lamps, 

 so shaped to hold the oil, has a yet more illustrious 

 history. It is a brachiopod, and, if that does not 

 amaze you, it is called terebratula. Many millions 

 of years ago all the bivalve molluscs were brachio- 

 pods and terebratula is a famous name to geolo- 

 gists. In our day, the pelecypods (oysters) rule 

 the bivalve world everywhere, and the brachiopods 

 are virtually extinct. All honour then to little 

 terebratula caput-serpentis for upholding so long 

 the dignity of its ancient family. 



