174 PHOLADIDZ. 
having I trust been satisfactorily disposed of, and every other 
part of the animal exhibiting a prototype similarity, it is 
impossible, as I think, to entertain further doubts of the 
positive identity of the two shells usually termed by authors 
Pholas papyracea and P. lamellata. I may add, that it has 
been asked in objection, how is it that twenty Pholadidea 
papyracea are taken for one Pholas lamellata, and that the 
two forms are not more frequently met with in the transition 
states? This objection quickly yields to a just view of the 
Pholades as regards habitat and other influences. 
The great mass of the Pholades inhabit the littoral and 
laminarian zones, and are thus open to the attacks of a multi- 
tude of enemies ; the delicate young papyracea suffer severely. 
My dredger, who for more than forty years has annually dug 
large quantities of all the species except P. crispata, states, 
that he constantly finds the shells of the young papyracea in 
their cavities, cleared out of the animal by minute species of 
Crustacea, in such quantities, that the dealers set them 
up with gum as a substitute for the rarer live examples, but 
the domed shells are rarely met with; still a portion escape 
to maintain the race, and some few young occasionally 
occur. I have personally taken them, i situ, m a decided 
transition state; it is necessary to observe that the crafty 
dealers produce this condition by mutilating the dome, but a 
lens will show the artful fracture or the natural progress of 
growth. 
I will say a few words on the pelagic Pholades mhabiting 
masses of stone dredged up in the littoral zones of the Devon 
coasts, six or eight miles from land. These shells, whether 
they are the two forms of Pholadidea papyracea, or the Pholas 
parva or P. dactylus, are always dwarf. I have a curious 
series of minute and completely adult Pholadidea papyracea 
not exceeding a } of an inch in length. Such shells are 
considered by the inexperienced observer as proofs that at all 
ages the Pholadidea papyracea is completely covered with a 
dome and continues gradually to increase: this is impossible, 
as when the dome and caliciform posterior extremity are once 
formed, all further growth is for ever terminated. The pelagic 
