6 Mr. W. Clark on the Terebrating Mollusca, and on the 



II. — On the Terebrating Mollusca. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



GENTLEMEN, Norfolk Crescent, Bath, Oct. 12, 1849. 



" Scire tuum, nihil e?t, nisi te scire hoc, sciat alter." 



This 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 in 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 qucestio of the boring functions 

 of the Acephala on the irrefragable bases of certainty ; and lastly, 

 I 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 oeconomy 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. In 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, 



