246 P. CRISPATA. 



deposited at the base of the cavity, below the body 

 of the industrious miner, a different plan is adopted. 

 Wherever a Pholas is at its labours, there are always 

 deposited within a circumference of several inches 

 round the" tunnel, myriads of short thin threads, 

 which are squirted out from the smaller siphon. 



The nodules on examination are found to be com- 

 posed of pulverized rock, which is drawn in at the 

 pedal opening, and ejected in the above manner, 

 thereby effectually clearing the lower portion of the 

 orifice. It was suggested to me that these thread- 

 like objects were the foecal matters of the Pholas, 

 but this idea was soon dispelled by the assistance of 

 the microscope; and, moreover, from the fact that 

 the threads are never visible when the animal is in a 

 quiescent state, but only when it is busily engaged 

 in its mysterious task of boring. 



I was for some time puzzled to find any aperture 

 in connection with the club-like foot of the Pholas 

 (P. crispata), although several of the bivalves were 

 sacrificed to the cause of science. But what the 

 microscope and scalpel in this instance failed to un- 

 fold, attentive watching of the animal in the aquarium 

 made palpably apparent, in the following manner. 



I had on one occasion captured about a dozen 

 Pholades, some of which were embedded in the solid 

 rock, others detached. 



The first mentioned, I knew would be quite safe 

 among the blennies and crabs, from the untempting 



