182 HALF AN HOUR WITH SHELL-FISH. 



whole bulk of the animal to bear a relation of con- 

 stantly increasing inequality to the whole capacity of 

 the shell. The subject is one of profoundest interest, 

 not only to naturalists, but also to mathematicians ; 

 and, although it is next to impossible for us to place 

 it before our non-mathematical readers in a more 

 simplified form, enough has been said to show what 

 important laws underlie such seemingly trivial things 

 as the shape and size of a univalve shell to the 

 mollusc that inhabits it. To quote Mr. Moseley's 

 own words again : " God hath bestowed upon this 

 humble architect the practical skill of a learned 

 mathematician !" 



We have purposely devoted the present chapter 

 to " Univalves," because the marine mollusca, even 

 of our British seas, are very numerous. It is next 

 to impossible for the sea-side visitor to take a walk 

 along the beach for any distance without seeing the 

 dead shells, both of bivalves and univalves, lying 

 about. Their size ranges from that of the large 

 red whelk, to the minute Rissoas and Kellias that 

 are only to be found by turning over the stones at 

 low water, and, even then, only by a sharp pair of 

 eyes. By the term " univalves " is usually meant 

 all those shells which are composed of one piece, as 

 the periwinkle, for instance. But it is found to be 

 impossible to draw a hard an4 fast line in natural 

 history anywhere, and it is equally so here. Many 

 of the shells now included under this general term 

 are in reality composed of many pieces, such as the 



