438 Mr STARK on Two Species of Pholas 



is little doubt, discover the arrangement by which these animals 

 are enabled to commence their cells. 



The Pholades, it may be remarked, seem admirably con- 

 structed for the purposes of their existence, so far as these are 

 known. Possessing but a comparatively fragile shell, which the 

 least force would break, and, having no weapons of defence 

 against their aquatic enemies, Nature has furnished them with the 

 means of amply providing for this apparent deficiency, by giving 

 them an asylum in the solid rock. Having formed their destined 

 habitations, which they can never leave, the rock is honeycombed 

 by successive races till it falls in pieces, and a new surface is expos- 

 ed for new generations. The tribes of Pholades on the different 

 coasts are thus active and powerful instruments in the disinte- 

 gration of rocks. The shale in which they occur at Joppa runs 

 in parallel and alternating strata, with a coarse sandstone ; and 

 while the unconnected ridges of the sandstone still appear, 

 rounded by the weather, or hollowed into basins by the action 

 of the waves, the alternating beds of shale have nearly disappear- 

 ed, through the instrumentality of these powerful, though un- 

 seen agents *. 



The Pholades are regularly used as an article of food on the 

 coasts of France and Italy, where they abound. In the neigh- 

 bourhood of Dieppe, bands of women and children, each armed 



* The disposition of the strata on the coast at Joppa, and its present appearance, 

 strikingly illustrates the power of the instruments which Nature has employed in the 

 disintegration of certain classes of rocks. The beds of shale, which in some places 

 seem to have been from 12 to 20 feet thick, have in most instances wholly disappear- 

 ed ; parallel roads or spaces, deeply covered with sand, and on a level with the neigh- 

 bouring shore, being alone left to mark out the places formerly occupied by the shale. 

 Dead shells, of very large size, are also frequently found on various parts of the coast, 

 or dredged up by fishing-boats ; thus affording indications, in the places where they 

 are found, of the disappearance of strata effected by their agency. Encrinites are 

 found in the shale at Joppa inhabited by the Pholades. 



