CARDIUM. 267 



the surface. When, on the contrary, the animal would 

 return to the light, it is only necessary to expand and 

 press its arm firmly against the sand, and the shell will 

 rise in proportion to the power exerted from beneath, 

 and will soon be disengaged. By this means the cockle 

 is also enabled to move both forwards and backwards, 

 but in a very limited degree. So far Reaumur. I 

 may also observe that the sand in which it lives is always 

 more or less saturated or infiltrated with water, and 

 sometimes is even semifluid, making it much easier for 

 the cockle to work its way than if it had to penetrate a 

 harder mass. The foot is very elastic ; and the pro- 

 digious leaps which the animal makes with it have been 

 noticed by many writers on popular science : Mr. 

 Gosse gives an amusing account of the feats which his 

 " Signor tuberculato" (C. tuberculatum) performed in 

 this way. The ridge-and-furrow sculpture is very re- 

 gular, and by means of this alternate arrangement each 

 valve locks closely into the other. Owing to the ad- 

 ductor muscles being but slightly attached to the shell, 

 the animal immediately becomes loose when put into 

 boiling or scalding water. Collectors therefore expe- 

 rience no trouble in cleaning the inside of any cockle- 

 shell. For this reason also live cockles are much more 

 easily opened than oysters, the latter operation being 

 rather an arduous undertaking to a bungling tyro. 

 They may have served to illustrate the proverb men- 

 tioned by Hesiod — /coyxyv SteXetv — signifying any slight 

 task. 



Very many species of Cardium occur in a fossil state. 

 Mr. Searles Wood says, " Species possessing undoubted 

 characters of this genus have been obtained from the 

 middle secondary formations, and they are largely deve- 



n2 



