Identity 0/ Pholadidea papyracea and Pholas lamellata. 11 



nature can do no more than perform the high behests of the 

 Deity, nor exceed those limits of action conlided to her by the 

 Great Kuler of the universe, who is the ens entium, and the first 

 cause of all that exists. 



1 revert to the boring MoUusca. Mr. Hancock has in many 

 consecutive pages taken the pains to show, that mechanical 

 boring, the solvents, and the ciliary currents, cannot be the causes 

 of excavation. 1 shall not for a moment dwell on these agents, 

 which are utterly worthless, and incapable of producing the effects 

 attributed to them ; but it may not be amiss to adduce some 

 further observations corroborative of Mr. Hancock^s position, 

 that the foot is the true terebrating agent. As regards the 

 Pholades, Saxicavce, and the Venerirupis jjerforans of authors, 

 they all inhabit the great littoral tracts of red sandstone on the 

 Devon coasts, near Exmouth ; this stone is composed of mole- 

 cular grains so feebly conglomerated, that there is not the least 

 necessity for the surface of the foot to be armed with siliceous 

 points ; the most gentle rubbing of that muscular coriaceous or- 

 gan will amply suffice to hollow out the cubicula of the molluscan 

 inhabitants of the red sandstone on the Devon coasts. The Pho- 

 lades at Exmouth, and 1 believe elsewhere, are rarely or ever 

 found in calcareous substances ; the Saxicavce are always in the 

 sandstone ; the Modiolina gastrochmna is never taken but in the 

 coralline zone, — I speak of Exmouth, — and bores both stones and 

 shells, as well as often forms its case of coarse agglutinated grains 

 of sand or corally spoil. When the Saxicavce and Modiolina gas^ 

 trochcEua are located in calcareous deposits, it is probable that 

 nature in this case provides the foot or mantle with siliceous 

 points ; but I think the attrition of the foot, aided by fine simple 

 sea-sand, is sufficient to rub down the cavities as fast as the ani- 

 mals grow. I corroborate by a thousand observations, that in 

 the Saxicavce and Modiolina gastrochcena, which have the foot 

 slender and feeble, their mantles are strengthened by the most 

 powerful muscular bands and fillets, which vary so much in 

 shape, disposition and intensity, that I have in some cases used 

 them successfully for specific distinction ; and I have not the 

 least doubt, as Mr. Hancock states, that this powerfully-armed 

 ventral portion of the mantle of the closed boring Acephala is 

 fully adequate to rub down their habitations. I believe that the 

 foot or mantle of the entire class of Acephala has the power of 

 terebrating, if circumstances require the exercise of it. It may 

 be observed that many of the Pholades are not in all circum- 

 stances borers ; many of them, — I may name the Pholas dactylus 

 and P. Candida at Exmouth, in the sandy districts, — ])ass their 

 entire existence in pure sand ; the same condition attaches to the 

 Venerirupis- perf Oram and many other bivalves. As to the borers 



