200 MULTIVALVES. 



Pholades were ranked by Linnaeus amongst the 

 multivalves, but by modern conchologists they 

 are generally placed with the bivalves. The 

 two principal valves connected by a hinge, 

 associate them closely to the latter, and the 

 small testaceous plates around the hinge may 

 be considered as mere appendages, for they do 

 not act the part of valves. The Pholas appear 

 the connecting link between the classes of 

 bivalves and multivalves. So gradual are the 

 steps by which the scale of nature proceeds, that 

 it is often difficult to ascertain precisely the 

 line which separates its great divisions, 



The Pholades are all borers, perforating wood, 

 clay, limestone, and sometimes burying them- 

 selves in the sand, forming a retreat in which they 

 pass their lives. The name marks their peculiar 

 propensity, being derived from (puXeos, (pholeos) 

 a hiding place. The largest species, and the finest 

 specimens are most frequently found in chalk, 

 which being the softest of calcareous substances, 

 admits of a more easy and rapid progress to the 

 animal than the indurated stones in which they 

 are sometimes discovered. How they effect 

 their lodgment, is still a subject of doubt and 

 inquiry. Many have supposed that a continued 

 rotatory * motion would in time produce such a 

 cavity as they inhabit, but as it is exactly fitted 

 to their size, it cannot be easily imagined that 

 the animal could perform this motion within it. 

 Another circumstance opposed to this opinion 



* Rotatory, like a wheel, from the Latin rota, a wheel. 



