Qapers^ Piddocks^ and Ship-z 



worms 



165 



who are constantly changing places. They seldom 

 interfere with each other by breaking through 

 their neighbour's party-wall, but as a rule make 

 their burrows to run parallel. The boring appears 

 to be effected by the flattened foot, assisted by the 

 rasp-like forepart of the shell in some species. The 

 native species are : — 



The Common Piddock (Pholas dactylus), the largest 

 by far of those found on our coast, its elongated shell 

 often measuring 5 inches in length. Each valve is 

 traversed by from 40 to 50 rows of prickly scales, 



Right valve of Common Piddock 



which are most developed in the front part. There 

 is a pale brown epidermis, but it is mostly worn 

 away except at the edges. The accompanying cut 

 shows the interior of a right valve of this species. 

 The hinge-plate, reflected over the beak in a double 

 fold, is strengthened beneath by a 

 number of transverse partitions, as 

 shown in this figure. Within the 

 shell there runs down from the 

 hinge-plate a curved shelly band, 

 called an apophyse, to which the muscles of the body 

 are attached. Upon the external folds of the hinge- 

 plate, what are known as the accessory valves are 

 placed ; but it must be remembered that these are 



Portion of hinge-plate 



