56 FEBRUARY. 



away the stone with the asperities with which the an- 

 terior parts of the valves are furnished. Between these 

 gentlemen a somewhat hot contention was maintained 

 for the honour of priority in this valuable discovery. 

 M. Cailliaud himself used the valves of the dead shell, 

 and imitating the natural conditions as well as he could, 

 actually bored an imitative hole, by making them rotate. 

 Mr. Robertson, at Brighton, exhibited to the public 

 living Pholades in the act of boring in masses of chalk. 

 He described it as " a living combination of three in- 

 struments, viz., a hydraulic apparatus, a rasp, and a 

 syringe." But the first and last of these powers can be 

 considered only as accessory to the removing of the de- 

 tritus out of the way, when once the hole was bored, 

 the rasp being the real power. If you examine these 

 living shells, you will see that the fore part, where the 

 foot protrudes, is set with stony points arranged in 

 transverse and longitudinal rows, the former being the 

 result of elevated ridges radiating from the hinge, the 

 latter that of the edges of successive growths of the 

 shell These points have the most accurate resem- 

 blance to those set on a steel rasp in a blacksmith's 

 shop. It is interesting to know that the shell is pre- 

 served from being itself prematurely worn away by the 

 fact, that it is composed of arragonite, a substance much 

 harder than those in which the Pholas burrows. Yet 



