138 Shell Life 



cavernous bulbs or so - called roots of the large 

 Laininarica. But it is only in parts of the west and 

 south-west that it need be looked for, such as the 

 shores of Cornwall, Scilly, Guernsey, Devon, Dorset, 

 Glamorgan, and Pembroke ; it also occurs round 

 Ireland, except on the north. Its zone is that of the 

 big seaweeds a little below extreme low water. The 

 form varies according to habitat. That figured is 

 the finest, and it lives either in rock chinks or in the 

 empty valves of Fholas dacfyliis. 



The Rock -borers (Petricola lithopliaga and P. 

 2jlioladifornilH) are not British, but they are found 

 occasionally on our shores. They bore into limestone 

 and mud. The first named 

 — which is also figured — is a 

 native of the Mediterranean 

 and the French coasts, but 

 „ , ^ /,, , • 7 7„ 7 N the second comes from North 



Rock-borer {Vvtncola uthoimoija) 



America. This, which has a 

 more elongated, more strongly ribbed shell than 

 P. lifhojyhaga, appears to have got established in 

 recent years about the estuary of the Thames and 

 in the river Crouch, Essex ; it has also been taken 

 at Heme Bay just above low water. It is very 

 probable that it has been introduced among oysters 

 that have been imported from America and laid 

 down in these districts. 



The Cockles are the British representatives of the 

 sub-order Cardiacea, which gets its name from the 

 conventional heart-shape (Karelia) of the closed shell 

 when viewed endwise. The two valves are exactly 

 alike, very convex, with prominent beaks, from 

 which strong ribs radiate. These ribs and the in- 



