THE SHELLS OF THE GULF OF CALIFORNIA. 



215 



We have taken a peep into the 0-shaped holes on the hack of our 



\V.Ji 



Gastrochcena, in situ. 



ipondylus valvr, broken arro-s; b, 

 in its burrow, valves closed, 

 shelly liniii" ot 



oyster; let us now see to what differences 

 the round holes are an index. The creatures 

 which leave these as their means of com- 

 munication with the outer world were called 

 Pholas by Linnaeus, and wore," the first 

 among the borers (if we except the ship- 

 worm, which long ago acquired even a 

 political importance from its ravages in 

 the Holland dykes) to attract the attention 

 of naturalists. They arc eaten on the 

 south coast of England, where they are 

 called Piddocks; and arc esteemed a dainty 

 morsel on the Californian shores, where 

 they go by the name of date fish. Our 

 oyster borers belong - to the section called 

 "Cup-pholas," from the capacious cup-like 

 appendage of delicate skin which rises 

 from the end of the shell in the English 

 species, (Pholadidea p'apyracea,) like a „ H) , 

 goblet resting on an alabaster pedestal, bivalve 



o~ . o . " ' showing large gape; 



and furnishes a receptacle into which the previous excavation ; h.,' siphon pipes, with 

 . . . i -ii i c ■ O-shaped opening ; \ t, inhalent and expel- 



siphon pipes may he withdrawn irom in- iant currents. 

 jury. To find this delicate fabric, with its translucent, elegantly- 

 sculptured valves, in the middle of the hard silicious rocks of the 

 New Red sandstone, must have been a puzzle both to the acid and the 

 valve-file theories. Our oyster-lover (other devourers of oysters de- 

 light themselves in the "savory fish;" this creature devours the shell) 

 is fashioned in a somewhat coarser mould; is somewhat wedge-shaped, 

 with the thin end of the wedge turned away from the seat of boring; 

 and, instead of one delicate capacious goblet, has a series of cup- 

 laminse, laid one over the other, on each valve, like the shingles or 

 tiles of a roof. Their extremely delicate structure would fare but 

 badly were the te to turn or the awl process the principal source of 

 oyster abrasion. During the adolescent or boring stage, the two 

 valves only touch each other at the point of the hinge, (where the 

 cartilage and teeth, so characteristic of ordinary bivalves, do not 

 exist.) and at a stout projecting knob on the ventral margin. It is 

 evident that then the powerful muscles of the foot, emerging from 

 the large anterior gape in the shell, have "ample room and verge 

 enough" to work from their hinge fulcrum, which is strengthened in 

 this family alone by a long spoon-shaped clavicle, enabling the animal 

 to direct its operations in many different points of attack. Having 

 rubbed and scooped all round in one direction, the valves have power 

 to twist and direct the undermining engine to another portion of the 

 cave. But when the creature has attained maturity, (and there are ■ 

 dwarfs and giants among these, as among men, it being common to 

 find adults not one-fourth the size of more highly pampered favorites 

 of the ocean,) it not only, like the Gastroclnena, and other Pholads, 

 lives retired from the world in its own burrow, but it lives retired 



