Gapers^ Piddocks^ and Ship-worms 



6i 



end ; the teeth are obsolete or wanting altogether ; 

 and the mantle impression shows only a shallow 

 sinus. They bore holes, chiefly in limestone, and 

 live in these cells with only their red siphons visible 

 at the entrance. 



The Wrinkled Eock- borer {S. rucjosa) is a very 

 common shell, yet it is very seldom seen save 

 by the conchologist, who knows where to 

 find it and how to chip it out from its cell 

 in the rock. The shell has an odd, distorted 

 appearance, being much stouter in front, and 

 pinched in the middle of the lower margin, 

 gaping behind or at each end, and with one 

 valve often larger than the other. It is 

 dirty white in colour, with a dull, rough 

 surface, irregularly wrinkled in concentric 

 fashion. The teeth, when present, are two small 

 erect cardinals in the left vah^e receiving one small 

 cardinal in the right valve. The animal 

 is whitish tinged with yellow. The 

 siphons — represented in our figure as 

 being retracted as far as possible — are 

 capable of great extension, and are 

 covered almost throughout their length by a brown 

 sheath, somewhat similar to that of the Gapers; 

 their extremities are red. Wherever chalk, limestone, 

 or red sandstone is found on our coast, there this 

 species may be looked for from a little below ordinary 

 low- water mark to a depth of about 30 fathoms. 

 When touched or alarmed it forcibly ejects a stream 

 of water from its siphons. A small variet}^, often 

 distinguished as a separate species {8. arctica), spins 

 a slight byssus and attaches itself to the so-called 



