218 THEIR HABITS 



will be obtained by supposing it to be made of 

 polished cornelian. This beautiful and versatile foot 

 is suddenly thrust out sideways, to the distance of 

 four inches from the shell. Then, its point being 

 curved backwards, the animal pushes it strongly 

 against any opposing object, by the resistance of which 

 the whole animal, shell and all, makes a considerable 

 step forwards. If the Cockle were on its native sands, 

 the leaps thus made would doubtless be more precise 

 in their direction, and much more effective ; but, 

 cooped up with its fellows in a deep dish, all these 

 herculean efforts availed only to knock the massive 

 shells against the sides, or roll them irregularly over 

 each other. 



It was curious to notice the extent to which the 

 interior of the Cockle was revealed, when the mouth 

 gaped, and the foot was thrust out. By the aid of a 

 candle we could see the interior surfaces of both 

 valves, as it seemed, almost to the very beaks. I say, 

 as it seemed, for so thin is the mantle where it lines 

 the shell, and so closely does it adhere to it, that 

 every character of the valves, whether as regards 

 colour or irregularity of surface, was distinctly visible ; 

 and thus we are able to distinguish the species, not 

 only by their external marks, but by one character 

 drawn from the interior ; — the ribs in tuherculatum 

 extending only half-way across the valves^ while in 

 aculeatum they reach back to the beaks. 



The former is much the finer species ; the valves 

 are more globose, and of a warmer colour ; those that 

 I have are even more spinous. The mantle is of a 

 rich deep orange, with elevated ribs, corresponding to 



