UNIVALVE MOLLUSCANS. 297 



beak and mouth of several give them no small 

 resemblance to the heads of certain birds, thus 

 one is called the thorny woodcock, 1 another the 

 snipe, 2 &c. 



At the first blush an inquirer into the use of 

 these spines and other arms of shell -fish, would 

 imagine that their object is defence, yet when 

 he is told that those which are most remark- 

 able for them, are themselves predaceous 

 animals; and that the herbivorous shell-fish 

 are usually not distinguished by any thing of 

 the kind, he seems to hesitate as to what con- 

 clusion he shall draw. It may be observed, 

 however, that the tribe most distinguished for 

 these arms, the rock-shells, are not so remarkable 

 for their size as many others which live by 

 prey, as the stroinbs, the helmet-shells, and the 

 tritons, so that their armour may sometimes 

 prevent one of these from boring their shells, 

 and inserting its proboscis into them. 



The tribe we are now considering, the rock- 

 shells, were in high esteem from the earliest ages 

 on account of the die that some of them af- 

 forded, and cloths died with it bore a higher 

 price than almost any other : more than one spe- 

 cies, however, yielded anciently a die ; one, ac- 

 cording to Bochart, a glaucous or azure colour, 

 as he interprets it, and the other purple. But 



' M. Tribulus. 2 M. Haustellum. 



