6 Mr. W. Clark on the Terebrating Mollusca, and on the 
Il.—On the Terebrating Mollusca. 
By Witi1am Crarx, Esq. 
To the Editors of the Annals of Natural History. 
GENTLEMEN, Norfolk Crescent, Bath, Oct. 12, 1849. 
“Scire tuum, nihil est, nisi te scire hoc, sciat alter.” 
‘Tus quotation, from one of the most sagacious of the satirists, 
is not meant to be applied here, as A. Persius employs it, to lash 
the inordinate vanities of authors craving to have their lucubra- 
tions committed to the press, but m its simple sense, as an in- 
contestable aphorism, that unless we communicate our ideas and 
what we know to others, our knowledge is vain and nought. In 
conformity with this application of the sentiment above, I pro- 
pose to state some important facts which I believe at present are 
not generally known relative to the boring Pholades and other 
Acephala, and particularly on the identity of Pholadidea papy- 
racea and Pholas lamellata of authors, together with some curious 
facts in the organization of the Bivalve Mollusca. 
To carry out these views, it will in the first place be necessary, 
to enable malacologists to form just conclusions on the matters I 
have sketched out, to furnish them with a correct account of the 
animals of Pholadidea papyracea and Pholas lamellata, accom- 
panied by a short summary of comparison, after which I trust I 
shall be able to place the vexata questio of the boring functions 
of the Acephala on the irrefragable bases of certainty ; and lastly, 
J shall communicate a most curious fact connected with the tes- 
taceous Acephala, which, if hitherto unknown and now established, 
must be considered most important, inasmuch as it will add a 
function of the first consideration to the ceconomy of these ani- 
mals. 
Pholadidea papyracea, Brit. Moll. 
Pholas papyracea, auctorum. 
Animal elongated, subcylindrical; mantle closed, except a 
small rayed aperture for the foot, as long as one exists, and 
which corresponds in position with a similar aperture in the 
membrane connecting the doming of the shell, and is styled by 
Dr. Turton a “ spiracle,” but which may perhaps in this species, 
the only one of the Pholades that has it, be for the purpose of a 
partial issue, or rather protrusion, without the solution of con- 
tinuity of the ventral membrane of the animal, of the hyaline 
cylindrical appendage which exists in all bivalves, to secure for 
it a point of support when the foot becomes so much diminished 
as not to afford one. Im all other bivalves this stylet is not 
visible, being imbedded in the body and upper part of the pedi- 
cle of the foot, which is the leaning-stock or point of resistance, 
