Mr. W. Clark on British Mollusca. 407 



inspect my collection of British shells, and to gratify me 

 with the sight of some of his own rarities. In so fruitful a 

 field for divergence of opinion, we differed and agreed again and 

 again. 



This conference, if you are pleased to allow me a little space 

 in your valuable Journal, will afford the opportunity I have 

 wished for to make some remarks on Mr. Jeffreys's " Gleanings 

 in British Conchology." I have very partially consulted that 

 gentleman on the observations I am about to offer; for when 

 the interests of science, as I think, are jeopardized, it at once 

 becomes the duty of the faithful observer to attempt to correct 

 error; and the more independently we exercise our opinions and 

 judgment, the better we shall succeed in searching out the truth, 

 and procuring the explanations and corrections which science 

 requires. 



That I may not exceed the ample limits you have afforded me, 

 I shall on this occasion only apply my remarks to those species 

 that appear to have the more pressing claims for attention, and 

 which, if passed over any longer without correction, may preju- 

 dice this branch of science. 



Mr. Jeffreys, in his "Gleanings" in the January 'Annals ' for 1858, 

 3rd series, vol. i. pp. .39-48. pi. 2. f. 2, has introduced a new species 

 with the appellation of Diodonta Barleei, captured by INIr. Barlee 

 off Arran Isle, county Galway. I was entirely unacquainted with 

 this, as I supposed, Irish species, until Mr. Jeffreys, seeing some 

 minute bivalves of Biploifonta rotundata on one of my tablets, de- 

 clared that they did not belong to that species, but were Diodonta 

 Barleei ; he made a minute of them, and the new habitat, Exmoutb. 

 I was greatly surprised at this very unexpected determination, and 

 on Mr. Jeffreys's departure I instituted a careful examination of his 

 discovery that my minute specimens oi Diplodonta were the Diodonta 

 Barleei. I found that Mr. Jeffreys had fallen into an error, and that 

 my shells were without doubt Diplodonta rotundata ; they pre- 

 sented all, even the minute attributes of that species, as the car- 

 dinal teeth, the absence of lateral ones, the adductor muscles con- 

 nected, as in it, by the circular pallial impression, showing in the 

 most decided manner its entirety, and absence of the sipbonal scar, 

 which denotes that posterior tubes do not exist in this animal — and 

 that fact I have shown in my own sketch of D. rotundata, figured 

 in the ' British Mollusca,' and accompanied by a description of the 

 soft parts, — whereas in the true Diodonta the siphonal scar is deep, 

 and more conspicuously pronounced than usual, denoting the pre- 

 sence of long siphons. My series of closed and open examples from 

 JL.th to ^ths of an inch, with a series of older shells, incontestably 

 corroborate this determination. The question that naturally arose 

 on this discovery was this, — Has Mr. Jeffreys mistaken my young 

 Diplodonta rotundata for the Diodonta Barleei 1 To ascertain this, 

 I wrote to Mr. Barlee for specimens ; but I failed to obtain them. I 



