THE SHELL-FISH OF THE COAST. 39 



ing the shell of Fetricola pholadiformis, and in which, 

 after the completion of the work of boring, the 

 projecting points on the shell are perfectly clear and 

 sharp, and not rubbed down as we should naturally 

 expect to find them after the hard work, of rock- 

 abrasion. Such a shell is the Pholas, of which three 

 species are represented on the Nesv Jersey coast. 

 The largest of these, Pholas costata (PI. 2, Figs. 21- 

 23), which measures about six inches in length, is 

 very generally represented only by fragments of the 

 shell, and it is still doubtful whether it normally 

 inhabits this part of the -coast. It is more properly 

 a species from the South (although observed as 

 far north as New Bedford), where it may be found 

 at some little distance beneath the surface in the 

 mud-banks which are exposed at low water. The 

 other two species, Pholas iruncata and P. crispata 

 (PI. 3, Figs. 1, 2), are very much smaller, and, while 

 their shells are ribbed anteriorly, they lack the full 

 series of spinose riblets which so regularly diversify 

 the shell of the larger form. In the latter species 

 the shell ' gapes' broadly at the two ends, the pos- 

 terior opening permitting of the extension of a very 

 powerful and muscular siphon. It is a common 

 habit with Pholas crispata to bore into rock, and 

 specimens of bored-rock fragments in museums 

 are not rare. The collections of the Academy 

 of ifatural Sciences of Philadelphia contain a re- 

 markable block of gneiss which is bored in this 

 manner. It has been sugge&t&d that the process 

 of boring may be entirely performed by the foot 

 taking up particles of sand and rubbing these 



