496 Mr. Jeffreys on British Mollusca. 



with still darker purple. There is a bright white zigzag 

 line on each side of the back of some large specimens. 

 Length nearly 6 inches ; 4 inches broad. 



The young is of a lighter purple, and may be mistaken for 

 another species. 



Found in deep water, Trincomalee. 



LI. — Notes on British Mollusca^ in answer to Mr. William 

 Clark's Remarks on " Gleanings in British Conchology" By 

 J. GwYN Jeffreys, Esq., F.R.S. 



To the Editors of the Annals of Natural History, 



Gentlemen, 



However much I may differ from Mr. Clark as to the limits of 

 specific and varietal distinction in the British Mollusca, I quite agree 

 with him in thinking that a free and independent discussion of the 

 subject must tend to promote the cause of science, and ultimately to 

 elicit the truth. Exoriatur aliquis who may be able to solve some 

 of these difficult problems ! 



In the 'Annals' for March last, p. 192, Mr. Clark has stepped 

 forward to the rescue of a species which he named Trochus Cutleri- 

 anusy but which I referred to the T. exilis of Philippi. I still con- 

 sider these species to be synonymous and identical ; and my opinion 

 is founded on the examination and comparison of many hundred 

 specimens, all of which appeared to me consistent with Philippi' s 

 description and figure. The comparative size of specimens and the 

 number of whorls differ in every univalve shell according to locality 

 and age ; and with respect to form, I believe it will be found that 

 the annexed figures (which are from 

 the accurate pencil of Mr. Sowerby) 

 agree much better with the one given 

 by Philippi than the figures in the 

 * British Mollusca,' to which Mr. 

 Clark has appealed, but which ma- 

 nifestly differ from each other. 



In the * Annals' for this month Mr. Clark has impugned some of 

 my discoveries, as well as those of Linnaeus, Lamarck, Forbes and 

 Hanley, Mr. Alder, and Mr. Bennett ; and I will answer his remarks 

 on each seriatim. 



Page 407. Diodonta Barleei. I am now satisfied, on reconsidera- 

 tion, that this is not a good species, but the fry of Biplodonta ro- 

 tundata. The form of young and adult individuals is so totally 

 different (in the one being triangular, and in the other suborbicular), 

 that it was only through the kindness of Mr. Searles Wood, who 

 fortunately had the requisite series of Crag specimens, that I was 

 enabled to reconcile this difference ; neither my own collection of 

 recent shells, nor any of those made by my numerous friends and 



