Identity of 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 confided to her by the 
Great Ruler of the universe, who is the ens entium, and the first 
cause of all that exists. 
I revert to the boring Mollusca. Mr. Hancock has in many 
consecutive pages taken the pais to show, that mechanical 
boring, the solvents, and the ciliary currents, cannot be the causes 
of excavation. I 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, Saxicave, and the Venerirupis perforans 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 I believe elsewhere, are rarely or ever 
found in calcareous substances ; the Saxicave are always in the 
sandstone ; the Modiolina gastrochena 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 Sazicave and Modiolina gas- 
trochena 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 Saxicave and Modiolina gastrochena, 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,—pass their 
entire existence in pure sand ; the same condition attaches to the 
Venerirupis perforans and many other bivalves. As to the borers 
